Science and Reason

A Galaxy Full of Surprises — NGC 3621 is bulgeless but has three central black holes

2011-11-29T17:36:00.000-08:00

A Galaxy Full of Surprises — NGC 3621 is bulgeless but has three central black holes

This image, from ESO’s Very Large Telescope (VLT), shows a truly remarkable galaxy known as NGC 3621. To begin with, it is a pure-disc galaxy. Like other spirals, it has a flat disc permeated by dark lanes of material and with prominent spiral arms where young stars are forming in clusters (the blue dots seen in the image). But while most spiral galaxies have a central bulge — a large group of old stars packed in a compact, spheroidal region — NGC 3621 doesn’t. In this image, it is clear that there is simply a brightening to the centre, but no actual bulge like the one in NGC 6744 (eso1118), for example.

NGC 3621 is also interesting as it is believed to have an active supermassive black hole at its centre that is engulfing matter and producing radiation. This is somewhat unusual because most of these so-called active galactic nuclei exist in galaxies with prominent bulges. In this particular case, the supermassive black hole is thought to have a relatively small mass, of around 20 000 times that of the Sun.

NGC 3621 – click for 1280×1280 image

The amino acid alphabet

2011-08-19T17:02:00.000-07:00

Amino acid alphabet soup

Via Astrobiology Magazine, 8/19/11

All living creatures on this planet use the same 20 amino acids, even though there are hundreds available in nature. Scientists therefore have wondered if life could have arisen based on a different set of amino acids. And what's more, could life exist elsewhere that utilizes an alternate collection of building blocks?

It really is rather remarkable that such a small subset of possible amino acids make up (almost) all the proteins in every known living organism on the planet. What enforces this strict discipline is the fact that all life forms on Earth use the same genetic code – a remarkable fact in itself – and this code does not specify any amino acids other than the same 20 ones. The way the code works makes substitutions impossible.

The reason for this inflexibility lies in the nature of transfer RNA, which is a critical part of the process in which genetic information encoded in DNA is converted to specific sequences of amino acids making up proteins. The DNA sequence of genes is first transcribed (in a process that is actually rather complicated) into another form of RNA – messenger RNA. All forms of RNA consist of a sequence of nucleotides, with every 3 nucleotides grouped together into "words". Since there are 4 possible nucleotides, there are 64 (=4³) possible distinct words.

In a molecule of transfer RNA, which typically comprises 73 to 93 nucleotides altogether, the three nucleotides at one end will match the sequence of one particular word of messenger RNA. The other end of the transfer RNA can bind to covalently to only one of 20 possible amino acids, completely ignoring any other amino acids. For any particular one of the 20 amino acids there are usually several different transfer RNAs that the amino acid can bind to, with each type corresponding to a specific 3-letter sequence of nucleotides. In this way there is a established a many-to-1 relationship between the 64 3-letter nucleotide words and the 20 amino acids. This is the genetic code.

The 20 amino acids can be considered as letters of another alphabet, in which sequences of letters (sometimes thousands of each) make up specific proteins. There are several interesting questions about this genetic code. Why are only 20 amino acids used, even though hundreds exist in nature? How did this small subset happen to be chosen – and be the same subset in all living organisms on Earth? If there is life on other planets that still encodes genetic information with DNA and RNA for making proteins, must the same 20 amino acids be used?

There is a range of possible answers to these questions. At one extreme, the subset of amino acids could have come about completely at random, perhaps being the first viable subset that emerged by chance and them became "frozen" in all successor life forms. At the other extreme, it could be that the amino acids actually used are the only ones that are able to build a suitable set of proteins. The intermediate case is that very early in the history of life many different subsets were in use, but in a process of evolution over time, the subset now used proved to be sufficiently superior to all others that it is the only one that survived in the conditions of the time.

Stephen Freeland and Gayle Philip performed a computer study to investigate whether the exact subset of 20 amino acids in the alphabet were more likely to be a completely random selection, or instead to represent a set that emerged as somehow the best suited for constituting the proteins of life on Earth. They reasoned that there were various properties any amino acid could have that would affect its suitability as a constituent of proteins. Among the properties were size and electric charge of the molecule, and the molecule's degree of attraction to water (hydrophilicity).

What they found was that the 20 amino acids actually occurring in proteins had a wide range of values for each of the properties, and that the range of properties was more evenly distributed over the subset than should occur if selection were random. In other words, the building blocks of proteins appear to be especially diverse in order to accommodate a large diversity of proteins that could be useful in living organisms. Thus evolution in the earliest stages of life on Earth probably favored the availability of many types of building blocks.

Abstract: Did evolution select a nonrandom "alphabet" of amino acids?: The last universal common ancestor of contemporary biology (LUCA) used a precise set of 20 amino acids as a standard alphabet with which to build genetically encoded protein polymers. Considerable evidence indicates that some of these amino acids were present through nonbiological syntheses prior to the origin of life, while the rest evolved as inventions of early metabolism. However, the same evidence indicates that many alternatives were also available, which highlights the question: what factors led biological evolution on our planet to define its standard alphabet? One possibility is that natural selection favored a set of amino acids that exhibits clear, nonrandom properties-a set of especially useful building blocks. However, previous analysis that tested whether the standard alphabet comprises amino acids with unusually high variance in size, charge, and hydrophobicity (properties that govern what protein structures and functions can be constructed) failed to clearly distinguish evolution's choice from a sample of randomly chosen alternatives. Here, we demonstrate unambiguous support for a refined hypothesis: that an optimal set of amino acids would spread evenly across a broad range of values for each fundamental property. Specifically, we show that the standard set of 20 amino acids represents the possible spectra of size, charge, and hydrophobicity more broadly and more evenly than can be explained by chance alone.

A Spiral in Leo

2011-08-10T23:59:00.000-07:00

A Spiral in Leo (8/10/11)

This new picture from ESO’s Very Large Telescope shows NGC 3521, a spiral galaxy located about 35 million light years away in the constellation of Leo (The Lion). Spanning about 50 000 light-years, this spectacular object has a bright and compact nucleus, surrounded by richly detailed spiral structure.

The most distinctive features of the bright galaxy NGC 3521 are its long spiral arms that are dotted with star-forming regions and interspersed with veins of dust. The arms are rather irregular and patchy, making NGC 3521 a typical example of a flocculent spiral galaxy. These galaxies have “fluffy” spiral arms that contrast with the sweeping arms of grand-design spirals such as the famous Whirlpool galaxy or M 51, discovered by Charles Messier.

NGC 3521 – click for 1280×1280 image

Actually, NGC 3521 looks a lot like NGC 2841.

More: here

Formation of earliest black holes

2011-08-06T02:57:00.000-07:00

Dawn of the black holes

(Science News) The seeds of the universe’s first black holes could have formed in gas halos much smaller than previously calculated, Canadian and American astronomers report online April 21 at arXiv.org. Simulated seeds about 100 times the sun’s mass were more common in massive gas halos, as expected (more mass means more stuff to collapse into a black hole). But because smaller halos may birth fewer stars — and fewer stars mean more pristine gas is available to collapse — seed formation could continue in smaller halos longer than in larger ones. The results jibe with two competing theories of supermassive black holes and could explain why some small galaxies have big black holes. —Camille Carlisle

The First Massive Black Hole Seeds and Their Hosts

Triple active galactic nucleus

2011-08-06T02:49:00.000-07:00

Black hole threesome revealed

(Science News) Andy Warhol reportedly said, “One’s company, two’s a crowd and three’s a party.” New data reveal one heck of a black hole party, a U.S. team of researchers reports online April 19 at arXiv.org. Three supermassive black holes — humungous gravity sinks that may form the cores of galaxies — and the stars around them could be crunching together to form a single galaxy, the group says. The first two galaxies should join up in 8 million years, with the third coming in about 32 million years after that. While scientists suspect that many galaxies have formed from such pile-ons, only one other possible triplet has been discovered so far. —Daniel Strain

Cosmic Train Wreck by Massive Black Holes: Discovery of a kpc-Scale Triple Active Galactic Nucleus

A Twisted Dust Web in the Galaxy IC 342

2011-07-24T20:44:00.000-07:00

A Twisted Dust Web in the Galaxy IC 342 (7/20/11)

Looking like a spiders web swirled into a spiral, the galaxy IC 342 presents its delicate pattern of dust in this image from NASAs Spitzer Space Telescope. Seen in infrared light, the faint starlight gives way to the glowing bright patterns of dust found throughout the galaxys disk.

At a distance of about 10 million light-years, IC 342 is relatively close by galaxy standards, however our vantage point places it directly behind the disk of our own Milky Way. The intervening dust makes it difficult to see in visible light, but infrared light penetrates this veil easily. It belongs to the same group as its even more obscured galaxy neighbor, Maffei 2.

IC 342 – click for 960×806 image

More: here, here

"Rose" of Galaxies

2011-07-08T23:25:00.000-07:00

"Rose" of Galaxies (4/20/11)

The newly released Hubble image shows a large spiral galaxy, known as UGC 1810, with a disk that is distorted into a rose-like shape by the gravitational tidal pull of the companion galaxy below it, known as UGC 1813. A swath of blue jewel-like points across the top is the combined light from clusters of intensely bright and hot young blue stars. These massive stars glow fiercely in ultraviolet light.

The smaller, nearly edge-on companion shows distinct signs of intense star formation at its nucleus, perhaps triggered by the encounter with the companion galaxy.

Arp 273 – click for 987×1000 image

More: here, here, here, here, here, here, here

Wide Field Imager view of a Milky Way look-alike, NGC 6744

2011-06-03T22:04:00.000-07:00

Wide Field Imager view of a Milky Way look-alike, NGC 6744 (6/1/11)

This picture of the nearby galaxy NGC 6744 was taken with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at La Silla. The large spiral galaxy is similar to the Milky Way, making this image look like a picture postcard of our own galaxy sent from extragalactic space. The picture was created from exposures taken through four different filters that passed blue, yellow-green, red light, and the glow coming from hydrogen gas. These are shown in this picture as blue, green, orange and red, respectively.

NGC 6744 – click for 1280×1078 image

More: here, here, here, here, here, here, here

A Perfect Spiral with an Explosive Secret

2011-06-03T21:51:00.000-07:00

A Perfect Spiral with an Explosive Secret (5/30/11)

This spiral galaxy was discovered back in the nineteenth century by French astronomer Édouard Jean-Marie Stephan, but in 2008 it became a prime target for observations thanks to the violent demise of a white dwarf star. The type Ia supernova known as SN2008a was spotted in the galaxy and briefly rivalled the brilliance of its entire host galaxy but, despite the energy of the explosion, it can no longer be seen this Hubble image, which was taken around a year and a half later.

NGC 634 – click for 1280×782 image

More: here

Flocculent spiral NGC 2841

2011-04-19T01:19:00.000-07:00

Flocculent spiral NGC 2841

Star formation is one of the most important processes in shaping the Universe; it plays a pivotal role in the evolution of galaxies and it is also in the earliest stages of star formation that planetary systems first appear.

Yet there is still much that astronomers don’t understand, such as how do the properties of stellar nurseries vary according to the composition and density of the gas present, and what triggers star formation in the first place? The driving force behind star formation is particularly unclear for a type of galaxy called a flocculent spiral, such as NGC 2841 shown here, which features short spiral arms rather than prominent and well-defined galactic limbs.

In an attempt to answer some of these questions, an international team of astronomers is using the new Wide Field Camera 3 (WFC3) installed on the NASA/ESA Hubble Space Telescope to study a sample of nearby, but wildly differing, locations where stars are forming. The observational targets include both star clusters and galaxies, and star formation rates range from the baby-booming starburst galaxy Messier 82 to the much more sedate star producer NGC 2841.

NGC 2841 – click for 1000×800 image

More: here, here, here, here

Telomerase can reverse the aging process... sort of

2011-02-27T19:25:00.000-08:00

Biologists are, at long last, beginning to understand the molecular processes responsible for aging in complex (multicellular) organisms – and to investigate ways to counteract these processes. We discussed one line of research in this recent article about a particular sirtuin (SIRT3) that helps relieve oxidative stress that can lead to DNA damage, which generally leads, in turn, to cell senescence or death.

While oxidative stress is certainly a significant factor in aging, possibly the most significant, there are others. One of these is the limitation on a cell's ability to undergo cell division in order to produce new cells of the same type. This is especially important in tissues that regularly need to regenerate, such as skin and intestinal tissue. Everyone now knows about telomeres, whose main function is to constitute protective end caps on chromosomes. The limitation on number of cell divisions happens since about 100 base pairs are lost from telomeres during each cell division. When telomeres eventually become too short signals that are similar to those associated with other kinds of DNA damage shut down a cell's ability to divide further. This mechanism indirectly helps mitigate the risks of DNA damage that are present every time a cell divides – an inherently tricky process.

However, this limitation on cell division isn't acceptable during embryonic development, when an organism's cell count is doubling most rapidly. So evolution has provided an enzyme – telomerase – that can rebuild telomeres, but is most active only during embryonic development. Except, of course, in cells that have become cancerous, where the ability to divide without limit is the name of the game. We discussed telomeres and telomerase in some detail a little over a year ago in this article, so you can go there for more.

Because of the risk of cancer, it seems imprudent to reactivate telomerase for the long term within an organism, especially in long-lived animals such as humans. (In animals like mice, which live fast and die young, it's a different matter. Telomerase may remain somewhat active in mice during adulthood. (Mentioned here.)) But what if it were possible to reactivate telomerase for a relatively short period of time (compared to the whole lifespan)... might that provide an opportunity to rebuild telomeres to some extent? Even better, might that reverse, at least to some extent, the ravages of aging?

We now have some research that seems to provide a fairly unambiguous affirmative answer... in a rather special case: Telomerase reactivation reverses tissue degeneration in aged telomerase-deficient mice.

But didn't we just say that mice may retain telomerase activity throughout their lives? Yes, however it's a relatively simple matter to "knock out" the main telomerase gene in mice (Tert). When that's done the resulting strain of knock-out mice – after several generations – have shortened lifespans and a general phenotype of age-related debilities, as one would expect. (The first few generations apparently still have sufficiently long teleomeres.)

Unfortunately, that's not a good enough model, since without a Tert gene, the organism has no way to manufacture telomerase. Simply giving the knock-out mice repeated infusions of telomerase is not a good way to ensure uniform distribution of the enzyme to all of the organism's cells. What to do? The experimenters came up with a rather clever solution. Normally the way that telomerase is activated in cells is by means of an "estrogen receptor" (ER), to which a form of the hormone estrogen (17β-estradiol to be precise) can bind and enable transcription of Tert. This ER can be tweaked so that estrogen binds to it only in the presence of another chemical, 4-hydroxytamoxifen (4-OHT).

A special form of the Tert gene that includes this special ER can be "knocked-in" to the mouse germline. It then turns out that 4-OHT can be efficaciously supplied to a TERT-ER mouse (in the form of a time-release subcutaneous pellet) to turn telomerase expression on and off at the experimenter's will. With that technology in place, the researchers were then able to perform a series of experiments demonstrating, in these special mice, that a month-long burst of telomerase could actually reverse a number of the ill effects of telomerase deprivation.

The first step was to show that without 4-OHT the TERT-ER mice (after a few generations) had many of the same problems, in the same degree, as later generations of knock-out mice that lacked Tert entirely. The TERT-ER mice (all of which were male) showed no signs of telomerase activity. Tissues in highly proliferative organs such as testes, spleen, and intestines showed notable atrophy. Lifespan of TERT-ER mice was about half that of normal ("wild type") mice.

The first test to investigate the effects of telomerase reactivation by means of 4-OHT was done in vitro. Fibroblast cells from TERT-ER mice were cultured and found to be essentially senescent and not undergoing cell cycles. But when the cells were placed in media containing 4-OHT, teleomerase was reactivated, telomeres lengthened, and cell proliferation resumed.

Some TERT-ER mice were then given a 4-week treatment of 4-OHT (subcutaneous pellets). At the end of that treatment there was a marked reversal of the degeneration that has occurred in testes, spleen, liver, and intestinal tissues, as well as resumption of sperm production. Survival time of these treated mice also increased. At the same time, 4-OHT had no effects on control mice that weren't lacking in telomerase and didn't have tissue degeneration.

Noteworthy results were obtained from tests to assess nervous system condition. Proliferation of neural progenitor cells was found to resume in TERT-ER mice treated with 4-OHT. Normal numbers of mature oligodendrocytes reappeared. Lastly, high-level neurological functions were restored, as indicated by resumption of nearly normal olfactory sensitivity.

An interesting conclusion that can be drawn from the neurological results is that neural progenitor cells probably survive loss of telomeres, so that they can rebuild neural cell populations if telomeres are repaired.

The really interesting question, of course, is the extent to which these results may apply, in some form, to humans. Unfortunately, there are a number of reasons to be skeptical. For one thing, telomere shortening is only one factor, and quite possibly not the main one, in human aging. Aging can be thought of as a complex disease, like cancer, with many contributing factors. The consequences of telomere truncation are only one factor.

Further, murine biology has signficant differences from human biology. Mice are less complex organisms, with rather short lifespans. Mice seem to retain some degree of telomerase activity throughout their lives, so they are not as well adapted to going for long periods without it.

It is noteworthy that evidence was not found that TERT-ER mice treated with 4-OHT became more susceptible to cancer. Still, mice don't live very long, and they are adapted to maintain active telomerase. Humans are different. If telomerase is artificially kept active for years in humans, incipient tumorigenicity could be accelerated.

Lastly, it's not necessarily easy to raise human telomerase activity levels in the first place. Although some telomerase-activating factors are known, they have not been tested extensively in humans for long periods of time, so their safety and efficacy profile is not known.

These research results are quite interesting – but they only indicate the need for much more investigation.

Jaskelioff, M., Muller, F., Paik, J., Thomas, E., Jiang, S., Adams, A., Sahin, E., Kost-Alimova, M., Protopopov, A., Cadiñanos, J., Horner, J., Maratos-Flier, E., & DePinho, R. (2010). Telomerase reactivation reverses tissue degeneration in aged telomerase-deficient mice Nature, 469 (7328), 102-106 DOI: 10.1038/nature09603

Further reading: (* = especially recommended)

* Telomerase reverses ageing process (11/28/10)

* The Curious Case of the Backwardly Aging Mouse (11/29/10)

* Partial reversal of aging achieved in mice (11/29/10)

Harvard scientists reverse the ageing process in mice – now for humans (11/28/10)

Gene reactivation reverses aging-related brain deficits in mice (11/30/10)

Age-Reversing Drugs on the Horizon? Not So Fast (11/29/10)

Telomere Tweaks Reverse Aging in Mice (11/29/10)

Alzheimers and aging advances uncovered (11/29/10)

An enzyme leads the dance of immortality and death (11/29/10)

Scientists Find Way to Partially Reverse Aging in Mice (11/29/10)

Supermassive black hole in a dwarf galaxy

2011-02-20T20:35:00.000-08:00

Supermassive black hole in a type of galaxy where nobody expected to find one? Henize 2-10 is a small, mostly unremarkable compact dwarf galaxy. Its estimated dynamical mass is about 10¹⁰ M_⊙, only a few percent of our galaxy's mass, and its distance from us is about 30 million light years. It is irregular in shape and does not fit in any category of the standard Hubble sequence.

The only respect in which Henize 2-10 has attracted attention – for several decades – before now is an extremely high rate of star formation in comparison to its size. The rate is 10 times that of the Large Magellanic Cloud, a satellite galaxy of the Milky Way that is also irregular in form and has approximately the mass of Henize 2-10.

This research – An actively accreting massive black hole in the dwarf starburst galaxy Henize 2-10 – recently published Nature, now offers good evidence that at the center of Henize 2-10 is an active black hole of substantial but somewhat uncertain mass between 2×10⁵ M_⊙ and 2×10⁷ M_⊙. That's a lot – it could exceed the mass of the Milky Way's black hole, ~4.2× 10⁶ M_⊙.

The evidence presented that Henize 2-10 contains an actively accreting massive black hole is pretty good. It includes detection of radio emissions with a substantial non-thermal component. In other words, much of the radio emissions is due to something besides black body radiation – perhaps synchrotron radiation typical in active black hole jets. There is also a point source of high-energy X-ray emissions coming from the same location as the radio emissions. The evidence that these emissions are due to an active black hole isn't perfect. In particular, long-baseline interferometry shows gaps in the radio source, and the radio spectrum does not have the shape of a typical radio galaxy's. But consideration of other possible explanations indicates that the alternatives are rather improbable.

However, the paper concludes "the massive black hole in Henize 2-10 does not appear to be associated with a bulge, a nuclear star cluster or any other well-defined nucleus. This unusual property may reflect an early phase of black-hole growth and galaxy evolution that has not been previously observed. If so, this implies that primordial seed black holes could have pre-dated their eventual dwellings."

The authors are implying that this black hole could have existed before Henize 2-10 itself. And further, since galaxies in the very early universe (z≥7) have many similarities to Henize 2-10 (as well as certain differences), that many of these very early galaxies could also have formed around pre-existing massive black holes.

These concluding observations should, on the basis of the evidence provided, be regarded as rather speculative. There are substantial logical gaps in the reasoning.

For one thing, Henize 2-10 is pretty unusual based on its high rate of star formation. This implies an unusual and probably chaotic recent history. And so there really isn't much solid reason to think that the central black hole predated the galaxy.

How closely Henize 2-10 resembles very early galaxies is also open to question. The earliest stars, which made up the earliest galaxies, had very low metallicity and therefore tended to be much larger, brighter, and short-lived than stars forming in the present era. The assumption that galaxy evolution would be pretty similar between now and then is hard to make.

Some of the popular media accounts go even further and suggest that "most" galaxies probably formed around pre-existing black holes. Even if that were true for Henize 2-10, all that can legitimately be inferred is the possibility, not the necessity, of that circumstance in most cases.

There have been reports of the existence of supermassive black holes in galaxies without central bulges (not just irregular galaxies) – here, for example. There have even been studies of active black holes in the early universe that may have predated their galaxies, one of which I wrote about in this article: Which came first - the galaxy or the black hole?. There are also cases of fairly normal galaxies, such as M33, that seem to have at most a very small central black hole – see here.

So it's certainly a very real issue whether, at least in some cases, central black holes form before their galaxies, but the present study is just another interesting data point, not the last word on the subject.

Reines, A., Sivakoff, G., Johnson, K., & Brogan, C. (2011). An actively accreting massive black hole in the dwarf starburst galaxy Henize 2-10 Nature, 470 (7332), 66-68 DOI: 10.1038/nature09724

Further reading:

Dwarf Galaxy Harbors Supermassive Black Hole – 1/9/11
Ginormous Black Hole May Solve Longstanding Mystery – 1/9/11
Baby Galaxy Hosts Monster Black Hole – 1/10/11
Astronomers Discover Supermassive Black Hole in Center of Tiny Galaxy – 1/9/11
Supermassive Black Hole Peeks From Behind The Skirt Of A Dwarf Galaxy – 1/10/11
Huge Black Hole Found in Dwarf Galaxy – 1/10/11
Henize 2-10: A Surprisingly Close Look at the Early Cosmos – 1/10/11
A Black Hole “Too Big” For Its Galaxy – 1/12/11
Supersized Black Hole Seen in Small Galaxy – 1/11/11
Dwarf galaxy solves supermassive mystery – 1/10/11
Dwarf galaxy hides a cosmic 'Little Big Man' – 1/10/11
New Evidence Shows Black Hole Growth Preceding Galactic Formation – 1/9/11
A tiny galaxy that hides a big secret – 1/11/11
Itty Bitty Galaxy Home to Gargantuan Supermassive Black Hole – 1/11/11
Massive black hole found in nearby galaxy – 1/11/11

Posts about sirtuins

2011-02-07T00:50:00.000-08:00

♦ Sirtuin proteins (11/16/07)

♦ The discovery of sirtuins, part 1 (11/17/07)

♦ The discovery of sirtuins, part 2 (11/20/07)

♦ Sirtuin news (1/21/08)

♦ SIRT1 and cancer (10/26/08)

♦ Testing the Fountain of Youth in the lab (2/7/11)

Testing the Fountain of Youth in the lab

2011-02-07T00:45:00.000-08:00

It's been more than 10 years since it was noticed that certain enzymes – the sirtuins – had life-extending properties in organisms like yeast, and later nematodes, fruit flies, and mice. The excitement spread to other compounds, such as resveratrol, that seemed to activate or assist sirtuins. Hopes were high that such things might offer the known longevity benefits of calorie restriction in a pill form. Ever since then the gold rush has been on to figure out how these things work – and if possible, to be the first to market with the Fountain of Youth in a bottle.

We've discussed sirtuins here a number of times before – here's a list of some of those discussions. If you need to brush up on the background, those would be good places to start.

The initial sirtuin that seemed to be most important for the longevity of yeast was SIR2. The gene for SIR2 is highly conserved in evolution – so it's probably kind of important. Homologs of SIR2 have been found in many sorts of higher organisms (nematodes, fruit flies, etc.). In mammals, including humans, there is a whole family of sirtuins, having at least 7 members, named SIRTx for x=1 to 7. ("SIRT" and "sirtuin" refer to SIR-two, where SIR was an acronym for "silent information regulator".)

SIR2 is primarily a histone deacetylase (HDAC), that is, an enzyme that removes acetyl groups from histone proteins (and often other types of proteins as well). Histones are the building block proteins that make up nucleosomes, around which DNA is spooled in chromosomes. Normally, DNA is tightly bound to the histones, which prevents the genes in the tightly bound portion of DNA from being transcribed into RNA in order to make proteins. In other words, the genes bound to a histone are effectively silenced. In order for a gene to be expressed, the histone closest to the portion of DNA containing the gene has to have an acetyl group attached at an appropriate location. Enzymes ("acetyltransferases") attach acetyl groups (in the process called acetylation) to histones in order to allow gene expression. Consequently, deacetylase enzymes, such as several sirtuins, are able to silence genes by removing acetyl groups from histones.

SIRT1 is the most intensively studied mammalian sirtuin. Like SIR2, it is primarily a histone deacetylase that is active in a cell nucleus to silence a wide variety of genes. Since SIRT1 can silence a large number of genes, it affects many cellular processes. However, there is one additional complication. SIR2 and SIRT1 only have their deacetylation ability in the presence of a small molecule called NAD: nicotinamide adenine dinucleotide, and only when NAD has a net positive charge, due to the loss of one electron during the process of metabolism in which cells generate needed energy. NAD⁺ denotes this form of NAD. (The neutral form of NAD is denoted by NADH.) Because of the role of NAD⁺, SIR2 is said to be a "NAD⁺-dependent" histone deacetylase.

All this is important, because research over the past 10+ years has shown that the lifespan-extending properties of calorie restriction, especially in simple organisms like yeast and nematodes, seem to be related, at least sometimes, with the deacetylation properties of SIR2 in the presence of NAD⁺. When an organism is in a calorie restricted environment, metabolism slows down, and less NAD⁺ gets used up. As a result, there is more NAD⁺ around. So SIR2 is more effective. So genes are silenced that would otherwise be expressed. Silencing these genes seem to help an organism live longer when nourishment is not ample – so that it can survive until the buffet table is restocked.

In an organism on a normal (not calorie restricted) diet, up-regulating SIR2 or otherwise enhancing its gene-silencing abilities seems to compensate for decreased amounts of NAD⁺, and thereby achieves for the organism some of the anti-aging benefits of a calorie-restricted diet without having to go hungry.

The problem is that the expression of so many different genes can be affected by SIR2 deacetylation that it's difficult to identify which genes among these are actually useful for promoting longevity or retarding aging – especially in organisms more complex than yeast or nematodes.

Now, however, research has come out involving a much less studied mammalian sirtuin, SIRT3 – Sirt3 Mediates Reduction of Oxidative Damage and Prevention of Age-Related Hearing Loss under Caloric Restriction. (I recommend viewing this link, since the illustration on the page will be helpful in understanding what follows here.) In spite of caveats I'll mention toward the end, this is a very significant and well-done piece of research.

A number of properties of SIRT3 had already been observed prior to this latest research. It is, like SIRT1, also a NAD⁺-dependent deacetylase enzyme. But unlike SIRT1, its main activity is found in cell mitochondria instead of in the nucleus. Consequently, SIRT3 deacetylates mitochondrial proteins instead of histones.

Of particular interest, this SIRT3 activity was known to be associated with calorie restriction (CR), because of overexpression in CR conditions and presumably also because of the NAD⁺-dependence. For example, studies in mice have shown that CR increases SIRT3 expression in liver mitochondria. Further, in knockout mice without SIRT3 mitochondrial fatty acid oxidation problems are found. Under CR SIRT3 is also overexpressed in mouse heart cells and may protect these cells from oxidative stress-induced cell death. (However, in this case it's possible that the effect resulted from HDAC activity in the cell nucleus.) So SIRT3 seems to be associated with anti-oxidant activity. There is, additionally, mechanistic evidence that SIRT3 inhibits mitochondria-related carcinogenesis. For instance, knockout mice without SIRT3 are susceptible to breast tumors.

The latest research presents strong evidence that under calorie restriction SIRT3 is involved in suppressing oxidative damage. The evidence is based on studies of oxidative stress-induced cochlear cell death responsible for age-related hearing loss (AHL) in mice. AHL is a pretty typical example of health problems associated with aging – one that affects humans as well as mice. The research not only shows an association between SIRT3 and protection from oxidative damage, but goes deep into the apparent mechanism involved. A variety of different in vitro and in vivo experiments with knockout mice provide the evidence.

To begin with, at the highest level, the researchers found that SIRT3 is required along with CR to inhibit age-related cochlear cell death and hearing loss. The knockout mice used in this, and other in vivo experiments, had both copies of the SIRT3 gene knocked out. The rate of progression of AHL was first measured in wild type (WT) mice as controls. CR was found to delay or mitigate AHL in the controls – but not in the knockout mice. This implies SIRT3 is necessary for CR to inhibit the progression of AHL – there's no benefit of CR for this condition without SIRT3. Further, when the cochlear cells of the experimental mice were examined, it was found that CR retarded cell death in the control animals but not in the mice without SIRT3.

So the key process to be concerned with is progressive cell death related to aging. The next experiments showed that the cell death was the result of oxidative damage. A lot of other studies have shown that CR inhibits oxidative damage to DNA, proteins, and lipids in many types of mammalian tissues. In the present research this was confirmed by examination of DNA in cochlear, brain, and liver tissues of control mice. But CR did not inhibit oxidative damage in the same tissues of the knockout mice. So SIRT3 appears to be necessary for the inhibition of oxidative damage to DNA, which presumably was responsible for accelerated cell death.

The next issue needing to be addressed is the mechanism by which CR inhibits oxidative damage. It is known that a small molecule, glutathione, is the major small molecule antioxidant in cells. Glutathione can exist in two oxidation states – reduced (GSH) or oxidized (GSSG). A high ratio of GSH to GSSG protects other molecules in the cell from oxidative damage, and GSH predominates in the healthy mitochondria of young mice. Conversely, a low ratio of GSH to GSSG is a marker for oxidative stress and/or aging. In the present research, the GSH:GSSG ratio was tested in control and knockout mice under CR conditions, at the age of 5 months. In the mitochondria of inner ear cells, as well as in brain and liver cells, it was found that the GSH:GSSG ratio increased as a result of CR in control mice, but not in knockout mice. Once again the presence of SIRT3 was shown to be necessary for an effect.

Obviously, the next thing to look at is how the GSH:GSSG ratio is controlled. The enzyme glutathione reductase (GSR) is known to be responsible for converting GSSG to GSH. So what happens is that reactive oxygen species (ROS) get soaked up in converting GSH to GSSG, and GSR reverses this to convert GSSG back to GSH.

However, in order to work GSR requires another molecule, nicotinamide adenine dinucleotide phosphate (NADPH) to do its job. NADPH is nothing but NAD, which we encountered in connection with the HDAC function of SIRT1, with a phosphate group attached. Like NAD, NADPH also exists in an oxidized form, NADPH⁺. This latter molecule predominates in mitochondria, and needs to be converted back to NADPH for use by GSR. (All this activity is really just shuffling electrons from one place to another. The pairs of molecules that mediate the activity are called "redox couples".)

So, what is it that converts NADPH⁺ to the plain old NADPH that we need? Well, that task is handled by yet another mitochondrial enzyme, isocitrate dehydrogenase 2 (Idh2). Don't despair – this is the last step! There is just one wrinkle. Idh2 is normally found in an acetylated form, in which case it is inactive. It needs to be deacetylated in order to become active and convert NADPH⁺ to NADPH. And that is precisely where the deacetylation function of SIRT3 comes into play. The researchers hypothesized that SIRT3 was needed in order to activate Idh2.

In order to test the hypothesis, they first measured acetylation of Idh2 in the control mice, with both normal and CR diets. With a normal diet, acetylation of Idh2 was substantial, but with CR there was an 8-fold decrease of acetylation. So it only remains to find the reason for that. In knockout mice, with no SIRT3, acetylation of Idh2 was "robust" with both normal and CR diets. That's a pretty good indication that SIRT3 was required for the effect. As a further indication, SIRT3 levels in the control mice were 3 times as high with a CR diet compared to a normal diet.

So SIRT3 is necessary for deacetylation of Idh2 under CR conditions, but there's still the possibility that it isn't sufficient by itself. It's possible that CR has other effects that facilitate deacetylation – CR may cause expression or activation of other enzymes that are needed. It's also possible that CR has other effects that increase NADPH independently of Idh2.

What if NADPH levels were tested directly? It was found that in the control mice NADPH did increase in all tissue types tested when a CR diet replaced a normal one, but this effect was not found in the knockout mice.

Efforts were made to use biochemical experiments (in vitro) to determine whether SIRT3 alone is responsible for deacetylating Idh2 under CR conditions. For example, another sirtuin, SIRT5, is also a deacetylase that occurs in mitochondria. Could it be helping deacetylate Idh2? The biochemical experiments indicated this was not the case.

Unsurprisingly, both normal and knockout mice were found to be leaner when fed a CR diet. Is it possible that lower body mass, especially resulting from less fat tissue, had some role in the protection from oxidative damage resulting from a CR diet? Perhaps, but other factors like that certainly weren't sufficient, as it was pretty clear that SIRT3 (absent in the knockout mice) was necessary, at least as far as AHL is concerned. It's still possible that SIRT3 isn't necessary for anti-aging effects of CR in tissue types that weren't tested (i. e. other than inner ear, brain, and liver tissue), or in mammals other than mice. The case is pretty solid for AHL in mice, but obviously there are many other age-related conditions and other species that should be investigated.

I should apologize for all the biochemical details presented here, but at least they should give you a good indication of just how complicated the effects of CR on aging and longevity can be – and probably are. There's a whole lot of work yet to be done before a reliable anti-aging pill can be developed for humans. Enthusiastic claims that this research "could lead to" therapies to slow down aging in general are basically BS. Yeah, these findings will help, but a heck of a lot more will be needed as well.

(As an example of just how badly misleading journalists who write about this stuff can be, consider this report, which begins with the claim: "In a remarkable demonstration of the ability of calorie restriction to blunt the effects of aging, scientists at the University of Wisconsin-Madison have succeeded in delaying age-related hearing loss in mice." Although the research showed that calorie restriction can do this, it did not produce any new way to do it. Instead, it shows how CR probably works by showing how CR doesn't work if SIRT3 is absent.)

So what's the bottom line here? It's pretty clear from this and many other studies that oxidative damage in cells is a cause of cell death and therefore of various health problems associated with aging. Undoubtedly there are a number of other factors that contribute to aging-related problems, such as cell death due to other causes and weakening or disregulation of the immune system. And even in the case of oxidative damage, there are many ways it can come about, and also many ways it might be inhibited. If you think of aging as a complex disease, like cancer – a point of view that has its detractors – then there are bound to be many causes and contributing factors. And also many ways to inhibit or arrest the process. The example considered here is just one of many.

Someya, S., Yu, W., Hallows, W., Xu, J., Vann, J., Leeuwenburgh, C., Tanokura, M., Denu, J., & Prolla, T. (2010). Sirt3 Mediates Reduction of Oxidative Damage and Prevention of Age-Related Hearing Loss under Caloric Restriction Cell, 143 (5), 802-812 DOI: 10.1016/j.cell.2010.10.002

Further reading:

Scientists ferret out a key pathway for aging (11/18/10)

Calorie restriction delays age-related hearing loss, UW study finds (11/18/10)

Scientists ID key protein that links dietary restriction with healthy hearing, aging (12/16/10)

Calorie Restrictions Slow Aging by Enzyme Pathway (11/19/10)

What activates a supermassive black hole?

2011-01-16T20:05:00.000-08:00

There's good evidence that massive black holes exist at the centers of most large galaxies having a central bulge, and even within galaxies that lack a central bulge, are small, or have an irregular form. Such black holes can range in size up to more than 10 billion solar masses (M_⊙). Little is known about what the average or typical mass of a central black hole is, although most are probably a lot smaller, such as that of Sagittarius A* in our galaxy, which is only ~4.2×10⁶ M_⊙.

Four million solar masses is still pretty hefty, so such objects are usually called supermassive black holes (SMBHs), as opposed to black holes that form as supernova remnants and are only at most a few M_⊙. It's not known exactly how SMBHs form and evolve. One clue is that most seem to reside in non-dwarf galaxies with a regular shape and a noticeable central bulge. This suggests that SMBHs form and evolve in tandem with the bulge. However, there are exceptions, such as one discussed here: Supermassive black hole in a dwarf galaxy. Another survey of small (under 10¹⁰ M_⊙) inactive galaxies in the Virgo cluster found that at least 24% had an X-ray-emitting SMBH.

Since a black hole emits little or no radiation directly, even SMBHs are difficult to detect at distances of millions of light years, unless they are surrounded by a substantial amount of gas and dust that is heated enough in the process of falling into the SMBH that it can strongly emit radiation on its own or produce other detectable effects, like jets. Objects that fall in this category are active galactic nuclei (AGN). In most cases only SMBHs that are active as AGNs are readily detectable, so these are the only specimens we know much at all about.

I've discussed AGN a lot, most recently here, here, here, here, here.

In order to study how SMBHs form and evolve we pretty much have to rely on studies of AGNs, which can provide many clues about this issue. Unfortunately, we don't know much about what causes a relatively quiescent SMBH to become active and turn into an AGN. It's this latter question that's addressed, indirectly, by the research to be discussed here.

But first let's back up to SMBHs in general. There are several interrelated questions concerning their origin and evolution. What accounts for their formation and periods of rapid growth? Do they form before, after, or in parallel with the formation of the galaxies in which they reside? What stimulates their intense outbursts of energy as AGNs or quasars?

The most basic question is: What are the typical ways that SMBHs grow? Possible answers include merger between smaller SMBHs, slow but steady accretion of matter from the surrounding galaxy, or bursts of rapid accretion when substantial amounts of gas and dust are swept up by the SMBH.

Each of these questions, among others, stimulates intense debates among astrophysicists who study such things. These questions are interesting and important not just for their own sake. Since there is a lot of evidence that the evolution of a galaxy and of its central SMBH occur in tandem, understanding the evolution of the SMBH helps us understand that of the whole galaxy.

The research we're concerned with here was designed to study the question by surveying a large number of galaxies that can be examined in some detail because they are not too distant. In this case, that means having a redshift z≤1. That corresponds to a distance (measured in light travel time) of about 7.7 billion light years – a little more than half the size of the visible universe. Since the research needs to examine the visible form of the object, anything farther away is too distant for even the Hubble telescope to resolve in sufficient detail. Also, at z=1 all light from the visible part of the spectrum is shifted to infrared, which Hubble's optics aren't optimized for.

An AGN produces quite energetic radiation across most of the electromagnetic spectrum. So, at least in most cases, it is a sign of the rapid burst model of growth mentioned above. This is typically just a relatively short phase in the life of the galaxy-black hole combination – on the order of a hundred million years or so. That's based on the observation that only about 1% (very roughly) of large galaxies are in this phase, over the 13.7-billion year age of the visible universe. Whether this represents the only mode of growth, or even the bulk of it, is the big unknown. And of course, if there are SMBHs that grow by modes other than rapid accretion, we won't even detect them as AGN.

The standard model of AGNs, which is pretty well accepted by the astrophysical community, is that rapid accretion of interstellar gas and dust around a SMBH is what powers the AGN's "engine". Presumably, then, the AGN goes quiet when most of the available gas and dust has been consumed. But that leaves the question of what initiates the process in the first place. Since there are still many AGNs that are active in the universe out to z=1, so that the galaxies involved have been growing for at least 5 billion years since the early days of the universe, AGNs could not have been active for their entire lives. Therefore, something happened at some point to trigger the activity we observe now.

Astrophysicists want to know what that something is. At least initially, there is much more gas and dust spread throughout the galaxy than in the center. Something has to happen to cause that matter to lose its angular momentum so it can fall into the center. One popular hypothesis has been that this process is triggered by mergers between mature galaxies of roughly equal size, as the gas and dust perturbed by the merger falls inward and is swept up by the central black holes (which might merge themselves). Up until now, there has not been a large-scale investigation of this hypothesis.

Now we have one: The bulk of the black hole growth since z~1 occurs in a secular universe: No major merger-AGN connection. (Available at the arXiv: 1009.3265v2.)

A sample of 140 AGNs was selected for examination. Another sample of 1264 inactive galaxies, carefully matched in size, distance, etc. was also selected for comparison. The only reliable indication of an ongoing merger is a visible distortion of the object's shape, so this is taken as a proxy for the occurrence of a merger. However, the galaxies observed could be undergoing "minor" mergers that don't result in visible distortion (considering how far away most selected objects are). And on the other hand, there's no way to be sure that an object's observable distortion is due to a merger. So the conservative view is that this research is looking at the correlation between galaxy activity and distortion of shape.

There are two specific questions addressed by the research: (1) How many AGN have a distorted structure that appears to be the result of a galactic merger? (2) Do AGNs show any significant difference in terms of visible distortion from otherwise comparable inactive galaxies?

The first question is about whether mergers that produce distortions are a necessary condition for an AGN. Since fewer than 15% of AGNs have visible distortion, the answer is clearly "no". The second question concerns whether a merger that produces distortion is sufficient to trigger an AGN. Since there was no significant difference between AGNs and a control set of non-AGNs in terms of frequency of visible distortion, it seems that whatever causes a distorted form (such as a merger) is not a significant cause for triggering an AGN.

Bottom line: Not only are distortion-producing mergers unnecessary for triggering an AGN, they do not even seem to be a significant cause. One way to think of it is as a visible symptom of some underlying process that might otherwise be hard to detect. (A medical example would be a cancer, whose presence might be indicated by physical symptoms or biochemical markers in the blood.) In the present case, it appears that having a distorted form isn't a symptom usually exhibited by a galaxy when an AGN is present - and in fact, it doesn't predict the presence of an AGN at all.

It is important to be able to identify reliable symptoms, because a galaxy may have an AGN that is not readily detectable directly. Many AGNs are not intense radio sources, presumably because they do not have significant jet structures. And unless we are viewing the galaxy more or less face-on, radiation at shorter wavelengths can be blocked by a thick torus of gas and dust surrounding the central engine of the AGN.

Not all important questions are answered by this study. For example, galaxy mergers that do not significantly distort galactic structure – perhaps involving the cannibalism of a small galaxy by a large one – might play an important role in triggering an AGN.

The results of this research are surprising, because they seem to rule out distortion-producing galaxy mergers as an important cause of AGNs – the previous general assumption. However, it shouldn't be concluded that galaxy collisions can never produce AGNs, let alone SMBHs. There is still the question of whether a SMBH can form "from scratch" without some sort of "seed". It could be that very large black holes formed in the very first instants after the big bang, as "primordial" black holes. (See here, for example. Further possibility for the formation of seed black holes are discussed here.)

However, a simulation study reported last year in Nature (here) showed that in the early universe, SMBHs could form directly from galaxy collisions. But conditions at that time were very different – there was much more gas around that hadn't formed into stars, and a much larger single mass of gas could accumulate without forming stars. Time permitting, as usual, I'd like to discuss this research in another post.

Cisternas, M., Jahnke, K., Inskip, K., Kartaltepe, J., Koekemoer, A., Lisker, T., Robaina, A., Scodeggio, M., Sheth, K., Trump, J., Andrae, R., Miyaji, T., Lusso, E., Brusa, M., Capak, P., Cappelluti, N., Civano, F., Ilbert, O., Impey, C., Leauthaud, A., Lilly, S., Salvato, M., Scoville, N., & Taniguchi, Y. (2011).
THE BULK OF THE BLACK HOLE GROWTH SINCE Z~1 OCCURS IN A SECULAR UNIVERSE: NO MAJOR MERGER-AGN CONNECTION
The Astrophysical Journal, 726 (2) DOI: 10.1088/0004-637X/726/2/57

Cyclotomic fields, part 2

2011-01-05T19:00:00.000-08:00

In our previous article on cyclotomic fields we were talking about why the Galois group G of ℚ(μ_n)/ℚ is isomorphic to (ℤ/nℤ)^×, where n∈ℤ and μ_n is the group of n^th roots of unity, the roots of xⁿ-1=0 in some extension of ℚ. (Check here for a list of previous articles on algebraic number theory.)

So far we've shown that G is isomorphic to a subgroup of (ℤ/nℤ)^×. We still need to show it is actually isomorphic to the whole group, or equivalently that |G|, the order of G, which is equal to the degree of the field extension, [ℚ(μ_n):ℚ], actually equals |(ℤ/nℤ)^×|, which is φ(n), the number of positive integers less than and relatively prime to n.

The group μ_n is cyclic. Any generator of the group is, by definition, a primitive n^th root of unity. We let ζ be an arbitrary but fixed such generator. Then ℚ(μ_n)=ℚ(ζ). Let f(x) be the minimal polynomial of ζ. f(x)∈ℚ[x] is irreducible over ℚ. All other elements of μ_n are of the form ζ^a for some a∈ℤ, where a is well-defined modulo n. Further, ζ^a is a primitive n^th root of unity if and only if a is relatively prime to n, i. e. the greatest common divisor (a,n)=1. The degree of f(x) equals [ℚ(μ_n):ℚ] and |G|. At this point, all we know about these numbers is that they divide φ(n) (since |G| does).

The group homomorphism j:G→(ℤ/nℤ)^× was defined by the relation σ(ζ)=ζ^j(σ), for σ∈G. We showed that j(σ) is injective and independent of the choice of ζ. Hence G is isomorphic to a subgroup of (ℤ/nℤ)^×, and therefore the degree of f(x) (and [ℚ(μ_n):ℚ] and |G|) is ≤φ(n). G is isomorphic to a proper subgroup of (ℤ/nℤ)^×, i. e. not the whole group, if j is not surjective and the degree of f(x) is strictly less than φ(n).

As we noted last time, the problem here is that we don't yet know that all φ(n) primitive n^th roots of unity are zeroes of f(x), so that |G| and the degree of f(x) equal φ(n), and hence G(ℚ(μ_n)/ℚ) ≅ (ℤ/nℤ)^×. Stated another way, we don't yet know that the field homomorphism on ℚ(μ_n) induced by mapping ζ to ζ^a is actually an automorphism of the field, hence an element of the Galois group. It could fail to be if, say, the minimal polynomial of ζ^a is different from that of ζ, which could happen if the degree of f(x) is less than φ(n) because not all primitive n^th roots of unity are zeroes of f(x). In order to rule out this possibility, we will show that the degree of f(x) is ≥φ(n).

There are various ways to prove the isomorphism, and even a number of ways to prove that f(x) has φ(n) distinct roots, so its degree is ≥φ(n). Many of these proofs use machinery (such as discriminants, factorization and ramification of primes, etc.) that we haven't extensively discussed yet, so I'll avoid using such things in the proof. However, we'll get to these topics eventually, and also show a way to construct the automorphisms σ∈G explicitly – after finishing the proof that G(ℚ(μ_n)/ℚ) ≅ (ℤ/nℤ)^×.

So let's get started. The roots of the minimal polynomial f(x)∈ℚ[x] are all conjugates σ(ζ) for σ∈G, so f(x)=Π_σ∈G(x-σ(ζ)). Hence f(x) is monic (leading coefficient 1). The coefficients of f(x) are symmetric functions of all conjugates of ζ, so the coefficients are all left fixed by all σ∈G. f(x) divides xⁿ-1, so all its roots – the conjugates of ζ – are algebraic integers. So the coefficients are also algebraic integers (sums of products of powers of algebraic integers) – members of the ring of integers O_ℚ(ζ). They are also in the base field, since they're left fixed by G. A basic fact is that O_ℚ(ζ)∩ℚ = ℤ – any algebraic integer that lies in the base field is necessarily an integer of the base field. Hence f(x)∈ℤ[x].

Suppose that for any a∈ℤ relatively prime to n, i. e. (a,n)=1, ζ^a is also a root of f(x): f(ζ^a)=0. Since these ζ^a with 1≤a<n are distinct primitive n^th roots of unity if ζ is, and there are φ(n) of them, the degree of f(x), and hence |G|, is ≥ φ(n). But we already showed |G|≤φ(n), hence |G|=φ(n). Since G is isomorphic to a subgroup of (ℤ/nℤ)^×, we must actually have an isomorphism: G ≅ (ℤ/nℤ)^×.

So all we have to show is f(ζ^a)=0 for 1≤a<n and (a,n)=1. The first thing to note is that it suffices to prove this just for primes p with (p,n)=1. For suppose we had that. For general a with (a,n)=1, let p be a prime that divides a. Then (p,n)=1. Consider ζ^a/p. Since (a/p,n)=1, ζ^a/p is a primitive n^th root of unity with one fewer prime divisor in the exponent than ζ^a. So by induction on the number of prime divisors of the exponent f(ζ^a/p)=0. But if the result is true for prime powers of primitive n^th roots of unity that satisfy f(x)=0, then f(ζ^a)=0 since ζ^a=(ζ^a/p)^p. Alternatively, you can recall that (according to a theorem of Dirichlet), there are infinitely many primes p in the arithmetic progression a+nk for (a,n)=1 and k∈ℤ. Since ζⁿ=1, ζ^a=ζ^p for all such p.

So let p be prime and (p,n)=1. Then note that f(x)^p-f(x^p)∈pℤ[x] for any f(x)∈ℤ[x]. This can be proved by induction on the degree of f(x). Suppose the highest degree term of f(x) is Ax^m, with p∤A. Then (Ax^m)^p-Ax^mp∈pℤ[x] because A^p≡A (mod p), because (ℤ/pℤ)^× is cyclic of order p-1 (Fermat's theorem). So if h(x)=f(x)-Axⁿ, then we just have to show h(x)^p-h(x^p)∈pℤ[x]. But that can be assumed true by induction, unless the degree of h(x) is 1. In the latter case, if h(x)=Ax+B, we need (Ax+B)^p-(Ax^p+B)∈pℤ[x]. But all the coefficients in (Ax+B)^p except the first and last contain binomial coefficients divisible by p, and the remaining terms are handled with Fermat's theorem as before.

Finally, then, suppose the opposite of what we want to show, namely that there is a prime p with p∤n and f(ζ^p)≠0. By what we just showed, f(ζ^p) is divisible by p in O_ℚ(ζ). We have f(x)=Π_i∈I(x-ζⁱ) for I={i∈ℤ: 1≤i<n and (i,n)=1}. So f(ζ^p) divides a product of nonzero factors ζ^p-ζⁱ. By a lemma we'll prove in a moment, if J={(i,j): i,j∈ℤ, 0≤i,j<n, i≠j}, Π_(i,j)∈J(ζⁱ-ζ^j) = (-1)^n-1nⁿ. Hence f(ζ^p) divides nⁿ and p|n, contrary to assumption. This contradiction means f(ζ^p)=0, as required. We've now shown f(x) has at least φ(n) roots, hence G(ℚ(μ_n)/ℚ) ≅ (ℤ/nℤ)^×.

Now for the last lemma: We have xⁿ-1=Π_0≤i<n(x-ζⁱ). Equating the constant terms gives (-1)^n-1=Π_0≤i<nζⁱ. And by taking derivatives of both sides, nx^n-1=Σ_0≤i<nΠ_{0≤j<n, j≠i}(x-ζ^j). Substituting x=ζ^k, nζ^k(n-1)=Π_{0≤j<n, j≠k}(ζ^k-ζ^j). Taking products of this for 0≤k<n gives, with the set J as above, Π_(i,j)∈J(ζⁱ-ζ^j) = nⁿ(Π_0≤k<nζ^k)^n-1. But the last product on the right side was evaluated above, so finally we are left with (-1)^n-1nⁿ on the right (since n-1 has the same even/odd parity as its square).

Well, that was a bit of work, wasn't it? But nothing too esoteric, apart from a little Galois theory and some classic number theoretical facts. (Thanks to [1, pp 96-8] for the bulk of the proof.)

Actually, it is possible to do this without the lemma, using the theorem on primes in an arithmetic progression. Suppose f(x) is any polynomial in ℤ[x] such that f(ζ)=0 when ζ is a primitive n^th root of unity. Then for any a∈ℤ with (a,n)=1, since f(x)^p-f(x^p)∈pℤ[x] for any prime p∈ℤ, we have 0=f(ζ)^p≡f(ζ^p) mod pO_ℚ(ζ). But there are infinitely many primes p≡a mod n, and for such p, ζ^p=ζ^a. Consequently, f(ζ^a) is a member of an infinite number of distinct prime ideals, which is possible only if f(ζ^a)=0. Hence f(x) has degree ≥φ(n), which is the crucial fact we found before.

We can now define the cyclotomic polynomial Φ_n(x)=Π_{0<i<n, (i,n)=1}(x-ζⁱ), for any primitive n^th root of unity ζ. From the foregoing, we know a lot about Φ_n(x): its roots are precisely all the primitive n^th roots of unity (in ℂ), its degree is φ(n), it is irreducible (over ℚ), its coefficients are in ℤ, and it is the minimal polynomial of ζ. The notation Φ_n(x) is on account of its relation to the Euler function φ(n).

We also have this factorization of xⁿ-1 in ℤ[x]: xⁿ-1 = Π_d|nΦ_d(x). This holds, since the roots of each Φ_d(x) are precisely the roots of unity in the cyclic group μ_n that have exact order d for each d that divides n. (Each root has one and only one exact order d satisfying d|n.) This relation is occasionally useful, and it yields interesting facts such as Σ_d|nφ(d) = n (by taking degrees of polynomials on both sides).

It turns out that the irreducibility of Φ_n(x) is relatively easy to prove for certain n, namely those that are powers of a single prime. So let p be prime and q=p^r for an integer r≥1. Let f(x)=Φ_q(x). The roots of f(x) are primitive q^th roots of unity, namely ζ∈μ_q such that ζ has order q. There are φ(q) of these and φ(q)=q-q/p=q(1-1/p)=(p-1)p^r-1 (because every p^th element of the set {0,1,...,q-1} is divisible by p). So clearly f(x)=(x^q-1)/(x^q/p-1). Let g(x)=(x^p-1)/(x-1) and h(x)=g(x+1)=((x+1)^p-1)/x=x^p-1+Σ_0<j<p(^p _j)x^j-1, where (^p _j) is a binomial coefficient, which is divisible by p if 0<j<p. Finally, consider the polynomial h(x^q/p)=g(x^q/p+1).

Suppose f(x) splits in ℚ[x]. Then since f(x)=g(x^q/p), the latter splits, and consequently g(x^q/p+1)=h(x^q/p) does too. But h(x^q/p) is what's known as an Eisenstein polynomial, because the leading coefficient is not divisible by p, the constant term is p (not divisible by p²), and all other nonzero coefficients (the binomial coefficients) are divisible by p. However, Eisenstein polynomials are irreducible over ℚ. This contradiction means f(x) must be irreducible over ℚ. QED.

The fact that Φ_q(x) is irreducible if q=p^r, and hence G(ℚ(μ_q)/ℚ)≅(ℤ/qℤ)^×, can be used as the basis for yet another proof of this isomorphism for arbitrary n, by considering prime power divisors q of n, the corresponding extensions ℚ(μ_q)/ℚ, and their Galois groups in building up the full extension ℚ(μ_n)/ℚ and its Galois group. But we won't go into that now.

In the next installment, we'll discuss many more fun facts about cyclotomic fields.

References:

[1] Goldstein, Larry Joel - Analytic Number Theory

A Great Ball of Stars

2011-01-03T01:55:00.000-08:00

A Great Ball of Stars (10/25/10)

The NASA/ESA Hubble Space Telescope has turned its sharp eye towards a tight collection of stars, first seen 174 years ago. The result is a sparkling image of NGC 1806, tens of thousands of stars gravitationally bound into a rich cluster. Commonly called globular clusters, most of these objects are very old, having formed in the distant past when the Universe was only a fraction of its current age. NGC 1806 lies within the Large Magellanic Cloud, a satellite galaxy of our own Milky Way.

NGC 1806 – click for 1280×788 image

Recent research findings on M87 (NGC 4486)

2010-12-28T17:00:00.000-08:00

M87 (Messier 87), also known as NGC 4486, is a giant elliptical galaxy, located about 53.5 million light-years away. It is noteworthy for several reasons, including the presence of an unusually large supermassive black hole (SMBH) in its active galactic nucleus, with an estimated mass of about 6.4×10⁹ times the mass of the Sun (M_⊙), two plasma jets that emit strongly at radio frequencies and extend at least 5000 light-years from the SMBH (although only the jet pointed more towards us is readily detectable), and a population of about 15,000 globular clusters.

The total mass of M87 is difficult to estimate, because elliptical galaxies like M87, and unlike spiral galaxies, do not tend to follow the Tully-Fisher relation between intrinsic luminosity and total mass calculated from rotation curves – which therefore includes dark matter. Estimates of the total mass of M87, including dark matter, come in around 6×10¹² M_⊙ within a radius of 150,000 light-years from the center. This compares with about 7×10¹¹ M_⊙ for the Milky Way, but M87 could be more than 10 times as massive.

In other comparisons, the Milky Way has only about 160 globular clusters, and a central black hole (Sagittarius A*) with a mass of about 4.2×10⁶ M_⊙. So M87's central black hole is about 1500 times as massive as the Milky Way's. Pretty impressive difference.

M87 – click for 640×480 image

Besides the recent research listed below, I've written about earlier research on M87 in these articles: Galactic black holes may be more massive than thought, Stellar birth control by supermassive black holes, Black holes in the news.

You might also be interested in some articles from the past year on the general subject of active galaxies: Active galaxies and supermassive black hole jets, Where the action is in black hole jets, Quasars in the very early universe.

Feedback under the microscope: thermodynamic structure and AGN driven shocks in M87 (6/29/10) – arXiv paper
Feedback under the microscope II: heating, gas uplift, and mixing in the nearest cluster core (3/28/10) – arXiv paper: Activity of the SMBH in M87 has a significant effect not only on the host galaxy, but also on the Virgo cluster of galaxies in which M87 is near the center. Energetic outflows of matter from near the black hole force plumes of gas out of the galaxy into the hotter intergalactic medium. The mass transported in this way represents about as much gas as is contained within 12,000 light-years of M87's center. (However, that's only about 2.5% of M87's 500,000 light-year radius.) If it had not been expelled, the gas could have formed hundreds of millions of stars.

The first paper reports on studies using the Chandra X-ray Observatory to measure gas temperatures around M87's center. The findings include detection of 2 distinct shock wave fronts about 46 thousand light-years and 10 thousand light years from the center. This indicates that explosive events occurred about 150 million and 11 million years ago, respectively.

The second paper uses observations from Chandra, XMM-Newton, and optical spectra to distinguish different phases of the hot gas surrounding M87's SMBH.

Refs:
• Galactic 'Super-Volcano' in Action (8/20/10) – Science Daily (press release)
• Galactic Supervolcano Erupts From Black Hole (8/20/10) – Wired.com
• Galactic 'Supervolcano' Seen Erupting With X-Rays (9/6/10) – Space.com
A correlation between central supermassive black holes and the globular cluster systems of early-type galaxies (8/13/10) – arXiv paper: A study of 13 galaxies, including M87, has found a correlation between the size of a galaxy's SMBH and the number of the galaxy's globular clusters. The types of galaxies studied included nine giant ellipticals (like M87), a tight spiral, and 3 galaxies intermediate in type between spiral and elliptical. The smallness of the sample is due to the exclusion of open spiral galaxies and the further limitation to cases where good estimates of the number of globular clusters and mass of the central black hole existed.

The correlation, in which the number of globular clusters is proportional to the black hole mass, is actually stronger than correlations between black hole mass and other galaxy properties previously studied for correlation, such as stellar velocity dispersion (an indicator of total mass), and luminosity of the galaxy's central bulge or whole galaxy (for ellipticals).

In some cases the correlation of black hole mass with total luminosity was especially weak, but better with number of globular clusters. For instance, Fornax A (NGC 1316) is a giant lenticular galaxy with luminosity comparable to that of M87. Yet its central black hole has a mass of 1.5×10⁸ M_⊙, 2.3% that of M87's black hole. It has 1200 globular clusters, 8% of M87's count. Clearly this is not a linear relation. Rather, the study found that the best fit was a power law with M_• ≈ (1.7×10⁵)×N^1.08±0.04, where M_• is black hole mass in units of M_⊙ and N is number of globular clusters. This relation predicts a SMBH mass of 5.5×10⁹ M_⊙ for M87, which is very close, and 3.6×10⁸ M_⊙ for the SMBH mass of NGC 1316, which is high – but the SMBH mass of NGC 1316 is also unusually low in comparison with its luminosity and velocity dispersion.

By contrast, the relation predicts that the Milky Way with a SMBH mass of 4.2×10⁶ M_⊙ should have only about 20 globular clusters, while the actual number is about 160. However, the Milky Way is a loose spiral, not one of the types that was studied, which may account for the much worse correlation. The fit is much better if only globular clusters associated with the central bulge (about 30) are considered.

The obvious question is about why this relation between SMBH mass and number of globular clusters exists. Presumably it has much to do with the typical history of a large galaxy, which is expected to include frequent mergers with other galaxies. The existence of the relationship should provide clues to galactic history, and especially how this may be different for loose spirals like the Milky Way, in comparison with more compact galaxies.

Refs:
• A correlation between central supermassive black holes and the globular cluster systems of early type galaxies (8/11/10) – The Astrophysical Journal
• Supermassive black holes reveal a surprising clue (5/25/10) – Physicsworld.com
A Displaced Supermassive Black Hole in M87 (6/16/10) – arXiv paper: It has generally been assumed that a galaxy's central SMBH is very close to the actual center of mass of the galaxy, because that is (by definition) the gravitational equilibrium point. This central point should be essentially the same as the photometric center of the galaxy, since the galaxy's stars should be distributed symmetrically around the center. Consequently, astronomers have not carefully searched for cases where a SMBH is not very near the galactic center. This lack of extensive investigation is also a result of the fact that the SMBH is often hidden inside a dense cloud of dust, so its exact position is difficult to determine. M87's SMBH (more precisely, the accretion disk around the SMBH), however, is clearly visible, and the research reported in this paper finds it is actually located about 22 light-years from the apparent galactic center.

There are various possible reasons for this much displacement from the center, and not a lot of evidence to identify the most likely reason. Possible reasons include: (1) The SMBH is part of a binary system in which the other member is not detected. (2) The SMBH could have been gravitationally perturbed by a massive object such as a globular cluster. (3) There is a significant asymmetry of the jets. (4) The SMBH has relatively recently merged with another SMBH, subsequent to an earlier merger of another galaxy with M87.

The displacement of the SMBH is in the direction opposite the visible jet, so the last two possibilities are more likely than the others. However, possibility (3) depends on the jet structure having existed at least 100 million years and the density of matter at the center of M87 being low enough to provide insufficient restoring force. Possibility (4) is viable if the SMBH is still oscillating around the center following a galactic merger within the past billion years.

Refs:
• A Displaced Supermassive Black Hole in M87 (6/9/10) – The Astrophysical Journal Letters
• Black Hole Shoved Aside, Along With 'central' Dogma (5/25/10) – Science News
• Black Hole Found in Unexpected Place (5/25/10) – Wired.com
• Supermassive black holes may frequently roam galaxy centers (5/25/10) – Physog.com (press release)
• Bizarre Behavior of Two Giant Black Holes Surprises Scientists (5/25/10) – Space.com
• Galactic Black Holes Can Migrate or Quickly Awaken from Quiescence (5/26/10) – Scientific American

M87 jet
Radio Imaging of the Very-High-Energy γ-Ray Emission Region in the Central Engine of a Radio Galaxy (7/24/09) – Science: Energetic plasma jets, in which matter is accelerated close to the speed of light, combined with intense electromagnetic emissions, especially at radio frequencies, are prominent in about 10% of active galaxies, including M87. However, little has been well established about what processes are responsible for the emissions, or more generally how the jets are powered, accelerated, and focused into narrow beams. Because of the relative proximity of M87 and the fact that the jet we observe is angled from 15° to 25° to our line of sight, M87 is one of the best objects to study in order to learn more about how jets work.

Gamma rays, because of their very high energies (greater than 100 keV per photon), are not continuously produced in active galaxy jets, but are occasionally observed in short bursts lasting only a few days. One such event occurred in M87 in February 2008. At the same time, the intensity of radiation at all other wavelengths increased substantially. Such flares, at lower energies, are not unusual, since the energy output of most jets is somewhat variable in time. The flare persisted for much longer at energies below the gamma-ray band, indicating that the disturbance continued to propagate along the jet even after the gamma-ray flare subsided. However, although we don't know what the cause was, the coincidence in time of the gamma-ray emissions and the beginning of the extended flare makes it very likely that the events had the same source.

This is significant information, because our technology for detecting gamma-ray events has very poor angular resolution (~0.1°), since gamma rays can be detected on the ground only by secondary effects that a gamma ray produces in our upper atmosphere. More than 6 orders of magnitude finer resolution can be achieved at radio frequencies, using very long baseline interferometry. With that technology, it was possible to locate the origin of the disturbance that caused both gamma ray and lower energy flaring to a region within about 100 Schwarzschild radii (R_s) of the SMBH. Since R_s = 2G×M_•/c², R_s for the M87 SMBH is about 1.9×10¹⁰ km, or more than twice the radius of the solar system. So 100R_s is about 70 light-days – which is pretty small compared to the 53.5 million light-year distance to M87.

It's also significant that the gamma-ray event occurred so close to the SMBH, because the cause must be unlike whatever is responsible for the flaring described in the following research.

Refs:
• VLBA locates superenergetic bursts near giant black hole (7/2/09) – Physorg.com (press release)
• Mysterious Light Originates Near A Galaxy's Black Hole (7/2/09) – Space.com
• A Flare for Acceleration (7/24/09) – Science
• High Energy Galactic Particle Accelerator Located (9/14/09) – Science Daily (press release)
Hubble Space Telescope observations of an extraordinary flare in the M87 jet (4/22/09) – arXiv paper: Electromagnetic radiation from SMBH jets is fairly variable in both time and location along the jet. In the case of M87, high-resolution images at various wavelengths have shown the existence of many regions of enhanced emissions within the jet. One of the most prominent of these even has a name: HST-1, so-named because it was discovered by the Hubble Space Telescope. It occupies a stationary position on the jet, about a million Schwarzschild radii from the center, i. e. about 2000 light-years from the SMBH.

HST-1 has been observable for some time, but until February 2000 it was relatively dormant. After that it began to flare more brightly across the electromagnetic spectrum up to X-rays. In 2003 it became more variable, and it reached its greatest brightness in May 2005, when the flux in near ultraviolet was 4 times as great as that of M87's central energy source, the SMBH accretion disk. This represents a brightness increase at that wavelength of a factor of 90. The X-ray flux increased by a factor of 50, and similar, synchronized changes occurred at other wavelengths. The synchronization indicates that one mechanism is responsible for the variability at all wavelengths.

What the actual cause of the disturbance may be is not clear. Because of the great distance of HST-1 from the SMBH, its basic energy source must not be the central accretion disk itself. More likely HST-1 is a result of constriction of magnetic field lines, resulting in further acceleration of the particles making up the jet. Acceleration of charged particles causes radiation by the synchrotron process, and is evidenced by polarization of the emitted photons. Constriction of the jet may be a result of passage through a region of higher density of stars. The increased variability could mean that the jet has encountered a region of higher but varying stellar density. Alternatively, the jet may be passing through a patch of thick gas or dust, with excess radiation produced by the resulting particle collisions.

These results could explain the variability of light from other, more distant active galaxies, at least those which have strong jets, given that it's possible for a small region of the jet far from the SMBH to outshine the central source. However, another source of variability occurs when a jet is viewed at a very low angle to our line of sight, in which case any slight change of direction could cause an apparent change of brightness.

Refs:
• Hubble Space Telescope observations of an extraordinary flare in the M87 jet (3/6/09) – The Astronomical Journal
• Hubble Witnesses Spectacular Flaring in Gas Jet from M87's Black Hole (4/14/09) – Physorg.com (press release)
• Black Hole Creates Spectacular Light Show (4/14/09) – Space.com
• Black hole jet brightens mysteriously (4/15/09) – New Scientist
• Black hole spews out impressive light show (4/20/09) – Cosmos Magazine

Pinwheel of Star Birth

2010-12-27T21:27:00.000-08:00

Pinwheel of Star Birth (10/19/10)

This face-on spiral galaxy, called NGC 3982, is striking for its rich tapestry of star birth, along with its winding arms. The arms are lined with pink star-forming regions of glowing hydrogen, newborn blue star clusters, and obscuring dust lanes that provide the raw material for future generations of stars. The bright nucleus is home to an older population of stars, which grow ever more densely packed toward the center.

NGC 3982 is located about 68 million light-years away in the constellation Ursa Major. The galaxy spans about 30,000 light-years, one-third of the size of our Milky Way galaxy.

NGC 3982 – click for 984×1000 image

More: here

Roots of unity and cyclotomic fields

2010-12-17T16:05:00.001-08:00

In preparation for many good things that are to come, we need to have a talk about another important class of field extensions of ℚ – the cyclotomic extensions. (Check here for a list of previous articles on algebraic number theory.)

A cyclotomic field in general is a field that is an extension of some base field formed by adjoining all the roots of the polynomial f(x) = xⁿ-1=0 for some specific positive n∈ℤ to the base field. Usually, though not always, this will mean roots that lie in some large field in which f(x) splits completely and that contains ℚ as the base field, such as ℂ, the complex numbers. f(x) is known as the n^th cyclotomic polynomial. Mostly the same theory applies if the base field is a finite algebraic extension of ℚ, but we'll use ℚ as the base field for simplicity.

Since f(1)=0, x-1 is one factor of f(x), and f(x)/(x-1) = x^n-1 + … + x + 1 ∈ ℤ[x], with all coefficients equal to 1. If n is even, -1 is also a root of f(x). However, all other roots of f(x) in ℂ are complex numbers that are not in ℝ. Some of these roots, known as the "primitive" n^th roots of unity – denoted by ζ_n (or just ζ if the context is clear) – have the property that all other roots are a power ζ^k for some integer k, 1≤k<n. So the smallest subfield of ℂ that contains ℚ and all roots of f(x) is ℚ(&zeta), known as the n^th cyclotomic field.

It is possible to express all the roots of f(x) in the form e^2πi/n, where e^z is the complex-valued exponential function, which can be defined in various ways. The most straightforward way is in terms of an infinite series, e^z = Σ_0≤n<∞zⁿ/n!. The exponential function e^z can also be defined as the solution of the differential equation dF(z)/dz = F(z) with initial value F(1)=e, the base of the natural logarithms. So there is the rather unusual circumstance that the roots of an algebraic equation can be expressed as special values of a transcendental function. Mathematicians long hoped that other important examples like this could be found (a problem sometimes referred to as "Kronecker's Jugendtraum", a special case of Hilbert's twelfth problem), but that hope has mostly not been fulfilled.

The most well-known nontrivial root of unity is the fourth root, i=&radic(-1), which satisfies x⁴-1 = (x²+1)(x²-1) = 0.

All complex roots of unity have absolute value 1, i. e. |ζ|=1, since |ζ| is a positive real number such that |ζ|ⁿ=1. The set of all complex numbers with |z|=1 is simply the unit circle in the complex plane, since if z=x+iy, then |z|² = x²+y² = 1. (Note that the linguistic root of words like "circle", "cyclic", and "cyclotomic" is the Greek κύκλος (kuklos).) Since e^iθ = sin(θ) + i⋅cos(θ) for any θ, with θ=2πk/n the real and imaginary parts of a general n^th root of unity ζ=e^2πi⋅k/n are just Re(ζ)=sin(2πk/n) and Im(ζ)=i⋅cos(2πk/n).

There are many reasons why cyclotomic fields are important, and we'll eventually discuss a number of them. One simple reason is that roots of algebraic equations can sometimes be expressed in terms of real-valued roots (such as cube roots, d^1/3 for some d), and roots of unity. See, for example, this article, where we discussed the Galois group of the splitting field of f(x)=x³-2.

The set of all complex n^th roots of unity forms a group under multiplication, denoted by μ_n. This group is cyclic, of order n, generated by any primitive n^th roots of unity. (Any finite subgroup of the multiplicative group of a field is cyclic.) As such, it is isomorphic to the additive group ℤ_n = ℤ/nℤ, the group of integers modulo n. Because of this, many of the group properties of μ_n are just restatements of number theoretic properties of ℤ_n. For instance, each element of order n in μ_n is a generator of the whole group – one of the primitive n^th roots of unity. Since μ_n⊆ℚ(ζ_n), adjoining all of μ_n gives the same extension ℚ(ζ_n) = ℚ(μ_n).

Now, ℤ/nℤ is a ring, and its elements that are not divisors of zero are invertible, i. e they are units of the ring. They form a group under ring multiplication, which in this case is written as (ℤ/nℤ)^× (sometimes U_n for short). An integer m is invertible in ℤ/nℤ if and only if it is prime to n, i. e. (m,n)=1 (because of the Euclidean algorithm). The number of such distinct integers modulo n is a function of n, written φ(n). This number is important enough to have its own symbol, because it was studied by Euler as fundamental to the arithmetic of ℤ/nℤ. Thus φ(n) is also the order of the group (ℤ/nℤ)^×.

Let ζ=e^(2πi)m/n, for 0≤m<n, be an element of μ_n. The correspondence m↔e^(2πi)m/n establishes a group isomorphism between the additive cyclic group ℤ/nℤ and the multiplicative group μ_n. Modulo n, m generates ℤ/nℤ additively if and only if (m,n)=1, which is if and only if the corresponding ζ generates μ_n. So the number of generators of μ_n – which is the number of primitive n^th roots of unity – is the same as the order of (ℤ/nℤ)^×, i. e. φ(n).

One has to be careful, because the multiplicative structure of μ_n parallels the additive structure of ℤ/nℤ, not the multiplicative structure of (ℤ/nℤ)^×. (Because if ζ^M and ζ^N are typical elements of μ_n then ζ^M×ζ^N=ζ^M+N.) Hence even though there are φ(n) generators of μ_n, these generators do not form a group by themselves (a product of generators isn't in general a generator), so the set of them isn't isomorphic to (ℤ/nℤ)^×, even though the latter also has φ(n) elements. Give this a little thought if it seems confusing.

Moreover, the group (ℤ/nℤ)^× is not necessarily cyclic. It is cyclic if n is 1, 2, 4, p^e, or 2p^e for odd prime p, but not otherwise. Confusingly, if the group does happen to be cyclic then integers modulo n that generate the whole group are called "primitive roots" for the integer n. If (ℤ/nℤ)^× happens to be cyclic, then only those m∈(ℤ/nℤ)^× having order φ(n) are "primitive roots" that generate the group, while all m∈(ℤ/nℤ)^× have the property that if ζ∈μ_n has order n and generates the latter group, then so does ζ^m, as we showed above. Got that straight, now? This needs to be understood when working in detail with roots of unity.

Another reason for the importance of cyclotomic fields is that the Galois group of the extension [ℚ(ζ_n):ℚ] is especially easy to describe. Indeed, it is isomorphic to the group of order φ(n) we've just discussed: (ℤ/nℤ)^×. There's a little work in proving this isomorphism, but let's first note what it implies. Let G=G(ℚ(ζ)/ℚ) be the Galois group. It is an abelian group of order φ(n) since it's isomorphic to (ℤ/nℤ)^×. Further, any subgroup of G′ of G is abelian and by Galois theory determines an abelian extension (i. e., an extension that is Galois with an abelian Galois group) of ℚ as the fixed field of G′. Conversely, it can be shown (not easily) that every abelian extension of ℚ is contained in some cyclotomic field. (This is the Kronecker-Weber theorem.)

Half of the proof of the isomorphism is easy. Pick one generator ζ of μ_n, i. e. a primitive n^th root of unity. We'll see that it doesn't matter which of the φ(n) possibilities we use. Suppose σ∈G is an automorphism in the Galois group. Since σ is an automorphism and ζ generates the field extension, all we need to know is how σ acts on ζ. Since σ is an automorphism, σ(ζ) has the same order as ζ, so it's also a primitive n^th root of unity. Therefore &sigma(ζ) = ζ^m for some m, 1≤m<n. As we saw above, m is uniquely determined and has to be a unit of ℤ/nℤ, with (m,n)=1, in order for ζ^m to be, like ζ, a generator of the cyclic multiplicative group μ_n. Hence m∈(ℤ/nℤ)^×. Call this map from G to (ℤ/nℤ)^× j, so that σ(ζ)=ζ^j(σ). To see that it's a group homomorphism, suppose σ₁,σ₂∈G, with j(σ₁)=r, j(σ₂)=s. Then σ₂(σ₁(ζ)) = σ₂(ζ^r) = (ζ^s)^r = ζ^sr, hence j(σ₂σ₁) = j(σ₂)j(σ₁). j is clearly injective since j(σ)=1 means σ(ζ)=ζ, so σ is the identity element of G. Finally, to see that j doesn't depend on the choice of primitive n^th root of unity, suppose ζ^m with m∈(ℤ/nℤ)^× is another one. Then σ(ζ^m) = σ(ζ)^m = (ζ^j(σ))^m = (ζ^m)^j(σ).

Thus G is isomorphic to a subgroup of (ℤ/nℤ)^×. That's enough to show G is abelian, so the extension ℚ(ζ)/ℚ is abelian. To complete the proof of an isomorphism G≅(ℤ/nℤ)^× we would need to show that the injective homomorphism j is also surjective, i. e. every m∈(ℤ/nℤ)^× determines some σ∈G such that m=j(σ). We can certainly define a function from ℚ(ζ) to ℚ(ζ) by σ(ζ)=ζ^m for a generator ζ of the field ℚ(ζ). One might naively think that's enough, but the problem is that one has to show that σ is a field automorphism of ℚ(ζ).

The map σ defined that way certainly permutes the n^th roots of unity in μ_n, the roots of the polynomial f(x)=xⁿ-1. However, not all permutations of elements of μ_n, of which there are n!, yield automorphisms of ℚ(ζ). The problem here is that if z(x) is the minimal polynomial of some ζ, i. e. the irreducible polynomial of smallest degree in ℤ[x] such that z(ζ)=0, then by Galois theory the order |G| of the Galois group G is the degree of the field extension, which is the degree of z(x). Since G is isomorphic to a subgroup of the group (ℤ/nℤ)^×, and the latter has order φ(n), all we know is that |G| divides φ(n). It could be that other primitive n^th roots of unity have minimal polynomials in ℤ[x] that are not the same as z(x), though they have the same degree |G|. For σ to be an automorphism, σ(ζ) needs to have the same minimal polynomial as ζ, and we don't know that immediately from the relation σ(ζ)=ζ^m.

We will defer discussion of the rest of the proof that G(ℚ(μ_n)/ℚ)≅(ℤ/nℤ)^× for the next installment, since some new and important concepts will be introduced.

Splitting of prime ideals in algebraic number fields

2010-12-13T19:21:00.000-08:00

Our series of articles on algebraic number theory is back again. Maybe this time it won't be so sporadic. Stranger things have happened. The previous installment, of which this is a direct continuation, is here. All previous installments are listed here.

When we left off, we were talking about how to determine the way a prime ideal factors in the ring of integers of a quadratic extension of ℚ. Such a field is of the form ℚ(√d) for some square-free d∈ℤ. We were using very simple elementary reasoning with congruences, and we found a fairly simple rule, namely:

If p∈ℤ is an odd prime (i. e., not 2), and K=ℚ(√d) is a quadratic extension of ℚ (where d is not divisible by a square) then

p splits completely in K if and only if p∤d and d is a square modulo p.
p is prime (i. e. inert) in K if and only if d is not a square modulo p.
p is ramified in K if and only if p|d.

The prime 2 behaves a little more weirdly, but the result is that 2 ramifies if and only if d≡2 or 3 (mod 4); 2 is inert if and only if d≡5 (mod 8); 2 splits if and only if d≡1 (mod 8).

One limitation was that our simple reasoning made it necessary to assume that O_K, the ring of integers of K, was a PID (principal ideal domain).

Let's review what we were trying to do. We were investigating the factorization of a prime ideal (p)=pO_ℚ(√d) in O_ℚ(√d). If O_ℚ(√d) is a PID, then there is a simple approach to investigate how p splits. If p splits then (p)=P₁⋅P₂, where P_i=(α_i), i=1,2. Any quadratic extension is Galois, and the Galois group permutes the prime ideal factors of (p). The factors are conjugate, so if α₁=a+b√d we can assume α₂=α₁*=a-b√d. Hence (p)=(α₁)⋅(α₁*)= (α₁α₁*)= (a²-db²).

Taking norms (to eliminate possible units ε∈O_ℚ(√d)) reduces the problem to a Diophantine equation of the form ±p=a²-db². With the problem thus reduced, a necessary condition for (p) to split (or ramify) is that the equation can be solved for a,b∈ℤ. A sufficient condition to show that (p) is inert, i. e. doesn't split or ramify, is to show that the equation can't be solved.

Let's look at how that might work. For example, let d=3. Looking at the equations modulo 3, we have ±p≡a² (mod 3). That is, either p or -p is a square modulo 3. Say p=5. The only nonzero square mod 3 is 1, and 5≢1 (mod 3). However -5≡1 (mod 3), so could we have -5=a²-3b²? Suppose there were some a,b∈ℤ such that -5=a²-3b². Then instead of looking at the equation modulo 3, we could look at it modulo 5, and find that then a²≡3b² (mod 5). If 5 divides either a or b, it divides both, and so 25 divides a²-3b², which is impossible since 25∤5. Therefore 5∤b. ℤ/(5) is a field, so b must have an inverse c such that cb≡1 (mod 5). Therefore, (ac)² ≡ 3(bc)² ≡ 3 (mod 5), and so 3 is a square mod 5. But that can't be, since only 1 and 4 are squares modulo 5. The contradiction implies -5=a²-3b² has no solution for a,b∈Z.

All that does show 5 doesn't split or ramify in ℚ(√3), hence it must be intert, but this approach is messy and still requires knowing that the integers of ℚ(√3) form a PID. We need to find a better way. Fortunately, there is one. But first let's observe that this elementary discussion shows there is a fairly complicated interrelationship among:

Factorization of (prime) ideals in extension fields,
Whether a given ring of integers is a PID,
Whether an integer prime can be represented as the norm of an integer in an extension field,
Whether an integer can be represented by an expression of the form a²+db² for a,b∈Z (in the case of quadratic extensions),
Whether, for primes p,q∈Z, p is a square modulo q and/or q is a square modulo p.

The problem of representing an integer by an expression like a²+db² is a question of solving a Diophantine equation, and more specifically is of the type known as representing a number by the value of a quadratic form. This question was studied extensively by Gauss, who proved a remarkable and very important result, known as the law of quadratic reciprocity, which relates p being a square modulo q to q being a square modulo p, for primes p,q.

We will take up quadratic reciprocity soon (and eventually much more general "reciprocity laws"), but right now, let's attack head on the issue of determining how a prime of a base field splits in the ring of integers of an extension field. We will use abstract algebra instead of simple arithmetic to deal with this question. For simplicity, we'll assume here that the base field is ℚ, even though many results can be stated, and are often valid, for more arbitrary base fields.

Chinese Remainder Theorem

The first piece of abstract algebra we'll need is the Chinese Remainder Theorem (CRT). Although it's been known since antiquity to hold for the ring ℤ, generalizations are actually true for any commutative ring.

Let R be a commutative ring, and suppose you have a collection of ideals I_j, for j in some index set, j∈J. Suppose that the ideals are relatively prime in pairs. In general that means that I_i+I_j=R if i≠j, and further, the product of ideals, I_i⋅I_j, is I_i∩I_j when i≠j. If R is Dedekind, then each ideal has a unique factorization into prime ideals, and they are relatively prime if I_i and I_j have no prime ideal factors in common when i≠j. Let I be the product of all I_j for j∈J, which is also the intersection of all I_j for j∈J, since the ideals are coprime in pairs.

The direct product of rings R_i for 1≤i≤k is defined to be the set of all ordered k-tuples (r₁, ... ,r_k), for r_i∈R_i, with ring structure given by element-wise addition and multiplication. The direct product is written as R₁×...×R_k, or &Pi_1≤i≤kR_i.

Given all that, the CRT says the quotient ring R/I is isomorphic to the direct product of quotient rings &Pi_1≤i≤k(R/I_i) via the ring homomorphism f(x)=(x+I₁, ... ,x+I_k) for all x∈R.

The CRT is very straightforward, since f is obviously a surjective ring homomorphism, and the kernel is I, since it's the intersection of all I_i. (It's straightforward, at least, if you're used to concepts like "surjective" and "kernel".)

Now we'll apply the CRT in two different situations. First let R be the ring of integers O_K of a finite extension K/ℚ, and I_i=P_i, 1≤i≤g, be the set of all distinct prime ideals of O_K that divide (p)=pO_K for some prime p∈ℤ. Then (p)=P₁^e₁ ⋅⋅⋅ P_g^e_g, where e_i are the ramification indices of each prime factor of (p). An application of CRT then shows that O_K/(p) ≅ Π_1≤i≤g(O_K/P_i^e_i). Recall that for each i, O_K/P_i is isomorphic to the finite field F_{q_i}, where q_i=p^f_i for some f_i, known as the degree of inertia of P_i. (This field is the extension of degree f_i of F_p=ℤ/pℤ.) Further, Σ_1≤i≤ge_if_i=[K:ℚ], the degree of the extension. Check here if you need to review these facts. Specifying how (p) splits in O_K amounts to determination of the P_i and the numbers e_i, f_i, and g.

The second situation where we apply CRT involves the ring of polynomials in one variable over the finite field F_p=ℤ/pℤ, denoted by F_p[x]. Let f(x) be a monic irreducible polynomial with integer coefficients, i. e. an element of ℤ[x]. Let f(x) be f(x) with all coefficients reduced modulo p, an element of F_p[x]. f(x) will not, in general, be irreducible in F_p[x], so it will be a product of powers of irreducible factors: Π_1≤i≤g(f_i(x)^e_i), where f_i(x)∈F_p[x]. Each quotient ring F_p[x]/(f_i(x)) is a finite field that is an extension of F_p of some degree f_i. In general, e_i, f_i, and g will be different, of course, from the same numbers in the preceding paragraph. But the CRT gives us an isomorphism F_p[x]/(f(x)) ≅ &Pi_1≤i≤g(F_p[x]/(f_i(x)^e_i)).

Now, here's the good news. For many field extensions K/ℚ, there exists an appropriate choice of f(x)∈ℤ[x] such that for most primes (depending on K and f(x)), the numbers e_i, f_i, and g will be the same for both applications of the CRT. Consequently, we will have O_K/(p) ≅ F_p[x]/(f(x)), because for corresponding factors of the direct product of rings, O_K/P_i^e_i ≅ F_p[x]/(f_i(x)^e_i). As it happens, most primes don't ramify for given choices of K and f(x), so that things are even simpler, since all e_i=1, and all factors of the direct products are fields.

We can't go into all of the details now as to how to choose f(x) and what the limitations on this result are. However, here are the basics. Any finite algebraic extension of ℚ (and indeed of any base field that is a finite algebraic extension of ℚ) can be generated by a single algebraic number θ: K=ℚ(θ), called a "primitive element". In fact, &theta can be chosen to be an integer of K. Then the ring of integers of K, O_K, is a finitely generated module over ℤ. (A module is like a vector space, except that all coefficients belong to a ring rather than a field.) The number of generators is the index [O_K:ℤ[θ]]. (ℤ[θ] is just all polynomials in θ with coefficients in ℤ.) If p∈ℤ is any prime that does not divide [O_K:ℤ[θ]], then the result of the preceding paragraph holds. If for some p and some choice of θ p does divide the index, then there may be another choice of θ for which p doesn't divide the index. Unfortunately, there are some fields (even of degree 3 over ℚ) where this isn't possible for some choices of p.

The situation is especially nice in the case of quadratic fields, K=ℚ(√d), square-free d∈ℤ. If d≢1 (mod 4); we can take θ=√d and f(x)=x²-d, since O_K=ℤ[√d]. If d≡1 (mod 4), then the index [O_K:ℤ[√d]]=2, and there's a possible problem only for p=2. However, we still have O_K/(p) ≅ F_p[x]/(x²-d) for all p≠2. From that it's obvious that, except for p=2, (p) ramifies if p|d, (p) splits if d is a square modulo p, or else (p) is inert. That is exactly the conclusion we began with at the beginning of this article, on the basis of elementary considerations. Only now we need not assume that O_K is a PID.

There are four important lessons to take away from this discussion.

First, there is a very close relationship between the arithmetic of algebraic number fields and the arithmetic of polynomials over a finite field. Not only do we have the isomorphism discussed above, but it turns out that a number of similar powerful theorems are true for both algebraic number fields and the field of quotients of polynomial rings over a finite field.

Second, a lot of the arithmetic of algebraic number fields can be analyzed in terms of what happens "locally" with the prime ideals of the ring of integers of the field.

Third, many of the results of algebraic number theory are fairly simple if the rings of integers are PIDs (or, equivalently, have unique factorization). Such results often remain true when the rings aren't PIDs, though they can be a lot harder to prove. Often the path to proving such results involves considering the degree to which a given ring of integers departs from being a PID.

Fourth, and perhaps most importantly, abstract algebra is a very powerful tool for understanding algebraic number fields – and it is much easier to work with and understand than trying to use "elementary" methods with explicit calculations involving polynomials and their roots.

We will see these lessons validated time and again as we get deeper into the subject.

So where do we go from here? There are a lot of directions we could take, so we'll probably jump around among a variety of topics.

Selected readings 11/28/10

2010-11-28T13:44:00.000-08:00

Interesting reading and news items.

Please leave some comments that indicate which articles you find most interesting or that identify topics you would like to read about, and I will try to include more articles of a similar nature in the future

These items are also bookmarked at my Diigo account.

Bad seeds, bad science, and fairly black cats?: Geneticists have failed to remind the public what the word “genetic” actually means. Heritability implies that gene and environment work, or might be persuaded to work, together. Why, after all, are taxpayers spending money on the double helix if there is no hope of an environmental intervention—a drug, a change in lifestyle, or cancer surgery after the early diagnosis of a somatic mutation—to help those at risk from what they inherit? Everyone in the trade knows this although they fail to mention it except to their first-year undergraduate classes. Transcripts of their lectures should be sent out with every press release. [The Lancet, 10/23/10]
Cancer’s little helpers: No one would have predicted a decade ago that these microRNAs, as the hairpins are called, were involved in cancer, because no one even knew that they existed in people. Mere snippets of RNA — DNA’s underappreciated cousin — these micromolecules are about 22 chemical letters long. But their size belies their power. [Science News, 8/28/10]
Hogan’s holometer: Testing the hypothesis of a holographic universe: In 2008, Fermilab particle astrophysicist Craig Hogan made waves with a mind-boggling proposition: The 3D universe in which we appear to live is no more than a hologram. Now he is building the most precise clock of all time to directly measure whether our reality is an illusion. [Symmetry Breaking, 10/20/10]
The Brain That Changed Everything: When a surgeon cut into Henry Molaison's skull to treat him for epilepsy, he inadvertently created the most important brain-research subject of our time — a man who could no longer remember, who taught us everything we know about memory. Six decades later, another daring researcher is cutting into Henry's brain. Another revolution in brain science is about to begin. [Esquire, 10/25/10]
How Big is the Unobservable Universe?: Based on what we currently think about inflation, this means that the Universe is at least 10^(1030) times the size of our observable Universe! And good luck living long enough to even write that number down. ... All that we know, see, and observe is just one tiny region that slid down that hill fast enough to end inflation, but most of it just keeps on inflating forever and ever. [Starts with a Bang!, 10/27/10]
Revealing the galaxy’s dark side: “In our paper, we discussed a number of astrophysical possibilities for the origin of the signal, including a population of pulsars, cosmic ray interactions and emission from our galaxy's supermassive black hole,” notes Hooper. “And in the end, no combination of any astrophysical sources could give us the signal we’re seeing,” he adds. “Eventually we just got fed up and concluded there doesn’t seem to be a way to explain the signal except for one thing — we tried dark matter and it fit beautifully without any special bells or whistles.” [Science News, 11/20/10]
When Muons Collide: A new type of particle collider known as a muon collider considered a wild idea a decade ago is winning over skeptics as scientists find solutions to the machine's many technological challenges. [Symmetry, 10/1/10]
We all need (a little bit of) sex: Sex costs amazing amounts of time and energy. Just take birds of paradise touting their tails, stags jousting with their antlers or singles spending their weekends in loud and sweaty bars. Is sex really worth all the effort that we, sexual species, collectively put into it? [Scientific American, 11/2/10]
Glia: The new frontier in brain science: Glia, in contrast to neurons, are brain cells that do not generate electrical impulses, and there are a lot of them—85 percent of the cells in the brain. Yet, these cells have been largely neglected for 100 years. I call this new frontier of neuroscience "The Other Brain," because we are only now beginning to explore it. The new findings are expanding our concept of information processing in the brain. They are leading rapidly to new treatments for diseases ranging from spinal cord injury to brain cancer to chronic pain, and Alzheimer's disease. [Scientific American, 11/4/10]
Extra neutrino flavor could be bitter end to Standard Model: What seems to have caught everyone's attention is the suggestion that this might be evidence of what are called sterile neutrinos. Although regular neutrinos barely interact with matter, sterile neutrinos can only interact via gravity, which (if they exist) is what has allowed them to escape our detection to date. Since they'd also be heavier than the regular neutrinos, they would make good dark matter candidates. [Nobel Intent, 11/2/10]
The Neanderthal Romeo and Human Juliet hypothesis: Scientists have had trouble reconciling data from analyses of human mitochondrial DNA and the male Y chromosome. Analyses of human mitochondrial DNA indicate that we all share a common female ancestor 170,000 years ago. Analyses of the Y chromosome indicate that we share a common male ancestor 59,000 years ago. How can we account for the idea that our common grandmother is 111,000 years older than our common grandfather? [Neuroanthropology, 10/26/10]
An idle brain may be the self's workshop: As neuroscientists study the idle brain, some believe they are exploring a central mystery in human psychology: where and how our concept of "self" is created, maintained, altered and renewed. After all, though our minds may wander when in this mode, they rarely wander far from ourselves, as Mrazek's mealtime introspection makes plain. [Los Angeles Times, 8/30/10]
Determining 500th Alien Planet Will Be a Tricky Task: At NASA's last count, astronomers had confirmed the discovery of 494 planets around alien suns. There are signs of dozens more, if not hundreds, but it will take time to weed out which of the detections are actual worlds and which are merely false alarms. [Space.com, 11/11/10]
Tracking Viruses Back in Time: How long have viruses been around? No one knows. Scientists at Portland State University have begun taking the first steps toward answering this question. [Astrobiology, 9/6/10]
Can a 1960s Approach Unify Gravity with the Rest of Physics?: In July mathematicians and physicists met at the Banff International Research Station in Alberta, Canada, to discuss a return to the golden age of particle physics. They were harking back to the 1960s, when physicist Murray Gell-Mann realized that elementary particles could be grouped according to their masses, charges and other properties, falling into patterns that matched complex symmetrical mathematical structures known as Lie groups. [Scientific American, 9/7/10]
Neuroscience: Settling the great glia debate: The consequences of this 'gliotransmission' could be profound. The human brain contains roughly equal numbers of glia and neurons (about 85 billion of each), and any given astrocyte can make as many as 30,000 connections with cells around it. If glia are involved in signalling, processing in the brain turns out to be an order of magnitude more complex than previously expected, says Andrea Volterra, who studies astrocytes at the University of Lausanne in Switzerland. Neuroscientists, who have long focused on the neuron, he says, would have to revise everything. [Nature News, 11/10/10]
This Is Your Brain on Metaphors: Symbols, metaphors, analogies, parables, synecdoche, figures of speech: we understand them. We understand that a captain wants more than just hands when he orders all of them on deck. We understand that Kafka’s “Metamorphosis” isn’t really about a cockroach. If we are of a certain theological ilk, we see bread and wine intertwined with body and blood. We grasp that the right piece of cloth can represent a nation and its values, and that setting fire to such a flag is a highly charged act. [New York Times, 11/14/10]
Tree or ring: the origin of complex cells: All complex life belongs to a single group called the eukaryotes, whose members, from humans to amoebas, share a common ancestry. Their cells are distinguished by having several internal compartments, including the nucleus, which shelters their precious DNA, and the mitochondria, which provide them with power. [Not Exactly Rocket Science, 9/12/10]
I am virus – animal genomes contain more fossil viruses than ever expected: Your closest fossils are inside you, scattered throughout your genome. They are the remains of ancient viruses, which shoved their genes among those of our ancestors. There they remained, turning into genetic fossils that still lurk in our genomes to this day. [Not Exactly Rocket Science, 11/18/10]
Effective Field Theory: "Effective field theory" is a technical term within quantum field theory, but it is associated with a more informal notion of extremely wide applicability. Namely: if we imagine dividing the world into "what happens at very short, microscopic distances" and "what happens at longer, macroscopic distances," then it is possible to consistently describe the macroscopic world without referring to (or even understanding) the microscopic world. [Cosmic Variance, 11/25/10]
Meet a superpartner at the LHC: Of the many ideas for new physics that can be tested at the Large Hadron Collider (LHC), supersymmetry is one of the most promising. The theory proposes that each fundamental fermion particle has a heavier bosonic superpartner (and vice versa for each fundamental boson) and by doing so, offers an extension of the standard model of particle physics that fixes many of its problems. None of the known particles appear to be superpartners, however, which leads to the daunting conclusion that if supersymmetry is correct, there are more than twice as many fundamental particles as we thought, but we have only been left with the lightest partners; that is, supersymmetry is broken. [Physics, 11/22/10]
Mafia Wars: An increasing amount of data is showing that the cellular battle between pathogens and hosts needs much more than a simple military metaphor to describe it—think undercover infiltration, front organizations, and forced suicide. [The Scientist, 6/1/10]

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Disturbing climate change headlines

2010-11-21T19:15:00.000-08:00

Yesterday Tom Yulsman at CEJournal came across a story in Fog City Journal that led to a brief post, on which I commented there.

The topic is the fraught question of what's the best way for scientists to respond to global warming Know-Nothingism. My first comment was followed by a response from Tom, and I've responded with a longer note that seems worth sharing here. It turns out that there is a great deal that needs to be said.

What follows is my second response, more or less verbatim.

Tom, I've read the Revkin article and the Feinberg/Willer paper. [See the press release for quick summary.] Thanks for the references. However, I don't find them very persuasive. Apologies in advance for the length of this note.

The Feinberg/Willer paper is based on the social psychology circle of ideas known as "Just World Theory" (JWT). Curiously, the book of the "founder" of JWT, Melvin Lerner, is entitled The Belief in a Just World: A Fundamental Delusion. Unfortunately, I don't have ready access to that volume, but I note that there is no question mark in the title, so I don't know whether Lerner himself actually regarded the underlying "just world" belief as a delusion.

Although the underlying belief that JWT deals with seems philosophically controversial (at best), JWT itself simply asserts that "many people" have this belief, and that certain consequences follow. One thing that concerns me is whether substantial evidence has been developed that quantifies how many people hold the underlying belief in the world's justness. At most it seems like just one dimension in a multidimensional space of belief systems.

It's clear enough that many people have religious beliefs that are incompatible with the idea that a "just" deity would allow the kind of climate developments that science predicts, and so such people deny the science. But that's a pretty broad feature of religion in general – it denies many kinds of science that clash with religion. So what's science supposed to do – give up and say, "Oops. we aren't really predicting what the evidence strongly indicates"?

The Feinberg/Willer paper argues that certain sorts of positive messages increase subjects' acceptance of the ideas (1) that the scientific evidence for global warming is good and (2) that science can find solutions to the problem. In other words, these messages are pro-science in a feel-good, non-threatening way. So of course it's not too surprising that the subjects who heard these messages exhibited greater acceptance of scientific conclusions. This is basic marketing theory.

One problem is that the part of the message that says science can find a "solution" to the problem is likely to be false. It's probable that there is no largely scientific solution. Mitigation of climate change is probably much more of an economic and political issue, because significant behavioral change and economic adjustment are likely to be necessary. Of course, this assertion is also open to debate.

I think that the best science has actually discovered a lot that suggests the threat of climate change is even more dire than some cautious observers assume. There is, for example, this: summary of ten rather disturbing types of climate threat reported in the past year.

You [Tom] wrote, "30 years of unrelenting fear appeals on climate change have gotten us, well, where? I would argue pretty much nowhere. If ever there was a prima facie case that fear appeals on climate change don’t work, this is it."

I'm afraid that by the very same sort of argument, 30 years of attempts to patiently and rationally educate the public on the science of climate change have also failed.

The real problem is that what's actually true is that different approaches work best with different types of people, depending on their undelying personality types and value systems. For example see Skeptics discount science by casting doubts on scientist expertise or the paper it discusses – Cultural cognition of scientific consensus.

One of the individuals that Revkin quotes in his article, Dan Kahan at Yale [and a founder of the Yale Cultural Cognition Project], states the problem quite well:

I think it [Feinberg/Willer] is good research, and maybe captures something that is going on in the real world debate. But it doesn’t capture what’s most important: the source of individual differences. People disagree about climate change; it is one of a cluster of science & policy issues that polarize citizens along cultural/political lines. "Just world" theory posits a general psychological mechanism that affects everyone. Necessarily, then, it can’t explain why one and the same set of informational influences (e.g., stories reporting "scientific consensus" on climate change) provoke different reactions in identifiable subcommunities. The theory that we need is one that identifies what the identifying characteristics of these communities are and how they are implicated in cognition of risk. No theory that focuses of [sic] generic or population-wide aspects of the psychology of risk perception (so-called "main effects") can do that.

In other words, a lot more needs to be done to steer public attitudes in the right direction. It is not a matter of simply finding the most comforting feel-good way to "frame" the issue, if that just entails obscuring the hard scientific facts. That is a vain hope.

I don't have a solution of the problem, but I think a solution should include a careful evidence-based appraisal of the kinds of messages that work best with different groups, combined with a plan for how to deliver the messages through different channels appropriate for different groups.

It's a lot like any other tough political campaign. Sometimes "negative" campaigning works very well, sometimes it doesn't.

I can see what's going on here. There are obviously efforts being made by a broad range of social scientists, communication experts, and journalists to shape an effective messaging strategy. For example: ClimateEngage.org. This is probably good. What is not clear is whether the people most involved will be able to identify a near-optimal strategy.

Just to name names, Matthew Nisbet [also here, here] (whom Revkin also quotes) is one with whom I find a lot to disagree – such as the whole "post-partisan" shtick. The elephant in the room is that most opponents of the necessity of acting on climate change – to say nothing of those who deny it even exists and/or is anthropogenic – have no intentions of operating in a reasonable and responsible "post-partisan" fashion.

There really is a war going on here. Climate scientists who don't face up to this reality are going to get the crap beat out of them. Just ask Phil Jones or Michael Mann [more here], for example. Much like Lt. Colonel George Custer at the Little Big Horn.

Young stars biting the cloud that feeds them

2010-11-01T00:16:00.000-07:00

Young stars biting the cloud that feeds them (8/30/10)

A billowing cloud of hydrogen in the Triangulum galaxy (Messier 33), about 2.7 million light-years away from Earth, glows with the energy released by hundreds of young, bright stars. This NASA/ESA Hubble Spare Telescope image provides the sharpest view of NGC 604 so far obtained.

Some 1500 light-years across, this is one of the largest, brightest concentrations of ionised hydrogen (H II) in our local group of galaxies, and is a major centre of star formation.

The gas in NGC 604, around nine tenths of it hydrogen, is gradually collapsing under the force of gravity to create new stars. Once these stars have formed, the vigorous ultraviolet radiation they emit excites the remaining gas in the cloud, making it glow a distinct shade of red. This colour is typical not only of NGC 604 but of other H II regions too.

NGC 604 – click for 1280×919 image

More: here, here

Selected readings 10/24/10

2010-10-24T15:40:00.000-07:00

The New Nu News!: There could be an extra, "sterile" neutrino out there, although cosmology places tight restrictions on that. There could be a fundamental difference between neutrinos and anti-neutrinos, which we don't (at present) understand at all. Or there could be some physics that's completely off the radar that explains this, but it looks like the good ol' standard model (and the simplest modifications to it) is woefully inadequate to explain what we're seeing. [Starts with a Bang, 9/27/10]
Primordial Magnetic Field May Permeate the Universe: Two physicists attempting to overcome some unexpected fuzziness in images of distant, supermassive black holes say they have found yet another potential big bang vestige: an extremely weak magnetic field that stretches across the universe. If scientists confirm the finding, it could help reveal the origins of magnetism in the cosmos. [ScienceNOW, 9/24/10]
The Itch of Curiosity: Curiosity is one of those personality traits that gets short scientific shrift. It strikes me as a really important mental habit - how many successful people are utterly incurious? - but it's also extremely imprecise. What does it mean to be interested in seemingly irrelevant ideas? And how can we measure that interest? While we've analyzed raw intelligence to death - scientists are even beginning to unravel the anatomy of IQ - our curiosity about the world remains mostly a mystery. [Wired, 8/3/10]
The Personality Paradox: There's an interesting new paper in Biological Psychiatry on the genetic variations underlying human personality. The study relied on a standard inventory of temperaments - novelty-seeking, harm avoidance, reward dependence and persistence - as measured in 5,117 Australian adults. What did the scientists find? Mostly nothing. The vast genetic search came up empty. [Wired, 8/9/10]
The Worm In Your Brain: So our cortex turns out to be a lot older than previously thought. The common ancestor of us and ragworms–a wormy creature that lived 600 million years ago–not only had a brain, but had an ur-cortex. And it probably used that ur-cortex to learn about its world–most likely learning about the odors it sniffed. That animal’s descendants diverged into different forms, and the ur-cortex changed along the way. Yet they still used many of the same genes their ancestor did long ago. [The Loom, 9/3/10]
Mapping the Brain on a Massive Scale: A massive new project to scan the brains of 1,200 volunteers could finally give scientists a picture of the neural architecture of the human brain and help them understand the causes of certain neurological and psychological diseases. The National Institutes of Health announced $40 million in funding this month for the five-year effort, dubbed the Human Connectome Project. Scientists will use new imaging technologies, some still under development, to create both structural and functional maps of the human brain. [Technology Review, 9/28/10]
Recipes For Limb Renewal: Bioengineers continue to refine prosthetic limbs, but they still can’t replicate the entire constellation of capabilities provided by flesh and blood. So a few determined scientists are pursuing a different solution: They are seeking the recipe for regrowing a missing limb. [Chemical & Engineering News, 8/2/10]
If low serotonin levels aren't responsible for depression, what is?: While traditional antidepressants do increase neurogenesis and relieve depression symptoms in some animal models, others show that neurogenesis and antidepressant behaviours are unrelated. Much of this debate comes down to the fact that we don't yet have a real understanding of neurogenesis, how it works, and how it is controlled both in normal brains and in the presence of antidepressants. Until we know, finding a truly effective antidepressant may remain out of reach. So while the monoamine/serotonin hypothesis for depression may be out, neurogenesis needs to step it up a little to make it in. [guardian.co.uk, 9/28/10]
A New Way to Make Stem Cells: A Harvard researcher has developed a way to make pluripotent stem cells that solves several of the major impediments to using them to treat human diseases. Derrick Rossi, an assistant professor at Harvard Medical School, created pluripotent stem cells--which can turn into virtually any other type of cell in the body--from non-stem cells without using viruses to tinker with a cell's genome, as conventional methods do. This means that Rossi's method could be substantially safer for treating disease. [Technology Review, 10/1/10]
Alien World Tour: The Exoplanets Around Star Gliese 581: The announcement Wednesday (Sept. 29) of two newfound alien planets circling the star Gliese 581 adds to the nearby solar system's intrigue, further cementing its status as a top candidate to harbor extraterrestrial life. One of the two newly discovered planets, known as Gliese 581g, is a small, Earth-like world that likely lies within its star's habitable zone - the just-right range of distances that allow liquid water to exist. Astronomers have now detected six planets orbiting Gliese 581, the most known to circle any star beyond our own sun. [Space.com, 9/29/10]
If There's Life on Alien Planet Gliese 581g, How Do We Find It?: After spending decades searching for alien planets capable of harboring life, astronomers may have found one. So how can they check to see if life actually exists on this alien world? ... One of the planet's discoverers said in a briefing yesterday that "the chances of life on this planet are 100 percent." To determine if this is true, researchers will have to scrutinize Gliese 581g from afar, searching its atmosphere for certain telltale molecules. But it might be a while before they have the tools to do this properly. [Space.com, 9/30,10]
Astronomer Seeks ET Machines: If we ever do receive a message from outer space, we’ll want to know what kind of aliens sent it. SETI researcher Seth Shostak says we shouldn’t expect them to be anything like us – in fact, they might not be biological at all, but instead, extraterrestrial machines. [Astrobiology Magazine, 10/1/10]
The Gates of Immortality: Why do cells allow some mistakes to accumulate? If evolution is such a powerful process-one that finds solutions to all manner of problems-how could there be processes or problems that can't be fixed? [The Scientist, 10/1/10]
The One True Path?: Niswender and Galli are elucidating a molecular link between mental illness and problems with how the body processes sugars. That link is part of the complex series of events that make up the insulin-signaling pathway, a crucial mechanism by which the pancreatic hormone insulin directs the transport and storage of glucose in virtually every cell type in the body. This is only one of a recent rash of discoveries about how insulin is also intricately involved in many disease processes, including the growth of cancer cells and defects in bone mass regulation. [The Scientist, 10/1/10]
A new source of CP violation?: Abazov et al. report an unexpectedly large value of the same-sign dimuon charge asymmetry. This means that they see pairs of positive muons, μ+μ+, among the debris of their proton-antiproton collisions more often than they see pairs of negative muons, μ-μ-. The key point is that their measurement violates CP symmetry, which relates the behavior of matter and antimatter particles. [Physics, 8/16/10]
Hagfish Analysis Opens Major Gap in Tree of Life: Since the 1970s, many evolutionary biologists have considered an eel-like, deep-sea-dwelling creature called the hagfish to be the closest extant relative of a last common ancestor for all backboned creatures. That made the hagfish a stand-in for a transitional species between invertebrates and higher animals, spanning a leap as dramatic as any in evolutionary history. But a new family tree based on high-powered molecular analysis lumps hagfish together with lampreys, a jawless fish that’s primitive, but very much a vertebrate. [Wired, 10/19/10]
On a quest to map the brain’s hidden territory: On a recent morning, Wedeen pulled up images created with the new technology, in which the lakes of white were crisscrossed by colorful, ropy bundles of fibers, revealing an elegant, three-dimensional architecture. Looking more like art than anatomy, these strands form the connections in the brain — the “connectome.’’ They are neural highways crucial for brain function, including thoughts, movements, and sensations. [The Boston Globe, 10/11/10]
The origin of complex life – it was all about energy: According to a new hypothesis, put forward by Nick Lane and Bill Martin, we are all natural-born gas-guzzlers. Our very existence, and that of every animal, plant and fungus, depended on an ancient partnership, forged a few billion years ago, which gave our ancestors access to unparalleled supplies of energy and allowed them to escape from the shackles of simplicity. [Not Exactly Rocket Science, 10/20/10]
The Fuel Of Evolution: Within the cells of humans and all other modern creatures are lots of tiny mitochondria, which may have been the key to the evolution of complex multicellular life billions of years ago. [InsideScience.org, 10/22/10]
Geologists revisit the Great Oxygenation Event: Why did oxygen levels spike 2.5 billion years ago, and how much oxygen was there in the atmosphere really? Why are banded iron formations made of layers only a few centimeters thick, and why did they stop forming so abruptly? If the oceans were oxygenated 2.5 billion years ago, why did multicellular life delay its appearance for another 2 billion years? And did all these changes really take place at pretty much the same time everywhere on Earth? [Physorg.com, 8/19/10]
Mirror Mirror On The Wall: Every one of the four forces of Nature we know of - gravity, electromagnetism, the weak force, and the nuclear force - all originate from slight variations of this narrative. Gauge symmetries are the origins of all the forces of Nature. For example, gravity arises from a gauge symmetry in 3D: a sphere of a gauge with its hand pointing in any direction in the full three dimensional span of space. [Schrödinger's Dog, 10/22/10]
Gravity Up Close: Scientists know how gravity works at big distances -- the inter-planetary or inter-stellar range -- but does it work the same way at the inter-atomic range? A variety of tabletop experiments are trying to explore this issue. Already some theorists say that a departure from conventional gravity behavior could hint at the existence of extra dimensions. [InsideScience.org, 10/13/10]
Cracks In The Universe: Physicists are hot on the trail of one of strangest theorized structures in the universe. A team of researchers have announced what they think are the first indirect observations of ancient cosmic strings, bizarre objects thought to have contributed to the arrangement of objects throughout the universe. [InsideScience.org, 10/11/10]

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An "Island Universe" in the Coma Cluster

2010-10-14T00:38:00.000-07:00

An "Island Universe" in the Coma Cluster (8/10/10)

A long-exposure Hubble Space Telescope image shows a majestic face-on spiral galaxy located deep within the Coma Cluster of galaxies, which lies 320 million light-years away in the northern constellation Coma Berenices.

The galaxy, known as NGC 4911, contains rich lanes of dust and gas near its center. These are silhouetted against glowing newborn star clusters and iridescent pink clouds of hydrogen, the existence of which indicates ongoing star formation. Hubble has also captured the outer spiral arms of NGC 4911, along with thousands of other galaxies of varying sizes. The high resolution of Hubble's cameras, paired with considerably long exposures, made it possible to observe these faint details.

NGC 4911 and other spirals near the center of the cluster are being transformed by the gravitational tug of their neighbors. In the case of NGC 4911, wispy arcs of the galaxy's outer spiral arms are being pulled and distorted by forces from a companion galaxy (NGC 4911A), to the upper right. The resultant stripped material will eventually be dispersed throughout the core of the Coma Cluster, where it will fuel the intergalactic populations of stars and star clusters.

NGC 4911 – click for 1280×1109 image

More here, here, here

An Elegant Galaxy in an Unusual Light

2010-10-04T00:20:00.000-07:00

An Elegant Galaxy in an Unusual Light (9/22/10)

A new image taken with the powerful HAWK-I camera on ESO’s Very Large Telescope at Paranal Observatory in Chile shows the beautiful barred spiral galaxy NGC 1365 in infrared light. NGC 1365 is a member of the Fornax cluster of galaxies, and lies about 60 million light-years from Earth. ...

The new infrared images from HAWK-I are less affected by the dust that obscures parts of the galaxy than images in visible light and they reveal very clearly the glow from vast numbers of stars in both the bar and the spiral arms. These data were acquired to help astronomers understand the complex flow of material within the galaxy and how it affects the reservoirs of gas from which new stars can form. The huge bar disturbs the shape of the gravitational field of the galaxy and this leads to regions where gas is compressed and star formation is triggered. Many huge young star clusters trace out the main spiral arms and each contains hundreds or thousands of bright young stars that are less than ten million years old. The galaxy is too remote for single stars to be seen in this image and most of the tiny clumps visible in the picture are really star clusters. Over the whole galaxy, stars are forming at a rate of about three times the mass of our Sun per year.

While the bar of the galaxy consists mainly of older stars long past their prime, many new stars are born in stellar nurseries of gas and dust in the inner spiral close to the nucleus. The bar also funnels gas and dust gravitationally into the very centre of the galaxy, where astronomers have found evidence for the presence of a super-massive black hole, well hidden among myriads of intensely bright new stars.

NGC 1365 – click for 1280×1271 image

More: here, here, here

A Galactic Spectacle

2010-09-30T01:13:00.000-07:00

A Galactic Spectacle (8/5/10)

The Antennae galaxies, located about 62 million light years from Earth, are shown in this composite image from the Chandra X-ray Observatory (blue), the Hubble Space Telescope (gold and brown), and the Spitzer Space Telescope (red). The Antennae galaxies take their name from the long antenna-like "arms," seen in wide-angle views of the system. These features were produced by tidal forces generated in the collision.

The collision, which began more than 100 million years ago and is still occurring, has triggered the formation of millions of stars in clouds of dusts and gas in the galaxies. The most massive of these young stars have already sped through their evolution in a few million years and exploded as supernovas.

The X-ray image from Chandra shows huge clouds of hot, interstellar gas that have been injected with rich deposits of elements from supernova explosions. This enriched gas, which includes elements such as oxygen, iron, magnesium and silicon, will be incorporated into new generations of stars and planets.

Antennae Galaxies – click for 851×864 image

More: here, here, here

Selected readings 9/28/10

2010-09-28T17:17:00.000-07:00

Convincing a Young Scientist that Dark Matter Exists: So I was in favor of dark matter, but I wasn't entirely convinced. I wanted a "smoking gun" piece of evidence for dark matter. Something that was an entirely new prediction that we could look for -- much like that 1919 eclipse was for general relativity -- and decide whether dark matter predicts what we're going to see. [Starts with a Bang, 6/24/10]
How blind to change are you?: This failure to notice what should be very apparent is something we unconsciously experience every day as our brains filter the barrage of visual information which we are flooded with. And apparently it has a name; it is called change blindness. [BBC News, 6/11/10]
New data suggest a lighter Higgs: New data offer evidence that the heft of the Higgs particle lies somewhere in the low end of the range being probed by particle colliders on two continents. The results also hint that the particle’s mass may be consistent with supersymmetry, a theory that gives every particle in the standard model of physics a much heavier partner. [Science News, 7/26/10]
Jellyfish eye genes suggest a common origin for animal eyes: Jellyfish may seem like simple blobs but some have surprisingly sophisticated features, including eyes. These are often just light-sensitive pits but species like the root-arm medusa have complex ‘camera’ eyes, with a lens that focuses light onto a retina. Not only are these organs superficially similar to ours, they’re also constructed from the same genetic building blocks. [Not Exactly Rocket Science, 7/27/10]
Astronomy and particle physics race to replace Standard Model: If energy issues seem to be attracting the attention of a lot of physicists, the Large Hadron Collider seems to be drawing the attention of many of the rest of them, including people in fields like cosmology, which deals with items on the opposite end of the size scale. In turn, the people working on the LHC and other particle detectors are carefully paying attention to the latest astronomy results, hoping they'll put limits on the properties and identities of the zoo of theoretical particles that need to be considered. [Nobel Intent, 7/28/10]
Genetics tells tall tales: Studies scanning the genomes of tens of thousands of individuals for gene variants associated with height have come up short: around 50 variants have been identified, but together they account for only 5% or so of height's heritability. ... This heritability may not be missing — it may simply be buried deeper than previously thought, in a multitude of genetic variants that have tiny effects individually. [Nature News, 6/20/10]
Dark matter eldorado: Observations confirm that a faint group of stars in the Milky Way’s backyard has the highest density of dark matter — the invisible material thought to account for 83 percent of the mass of the universe — of any galaxy known. [Science News, 7/30/10]
Searching through the LHC data flood for dark matter: Although the Standard Model has needed some minor tweaking to deal with recent observations, Gross said that there are three major issues that suggests it's due for a major overhaul. One of these is that we have convincing evidence that dark matter exists, and comes in the form of particles that are heavy and stable to at least the life of the Universe. Unfortunately, the Standard Model provides nothing that meets these requirements. [Nobel Intent, 8/1/10]
Two New Paths to the Dream: Regeneration: Animals like newts and zebra fish can regenerate limbs, fins, even part of the heart. If only people could do the same, amputees might grow new limbs and stricken hearts be coaxed to repair themselves. But humans have very little regenerative capacity, probably because of an evolutionary trade-off: suppressing cell growth reduced the risk of cancer, enabling humans to live longer. A person can renew his liver to some extent, and regrow a fingertip while very young, but not much more. [New York Times, 8/5/10]
Sponge genes surprise: A complete genetic catalog of the sponge Amphimedon queenslandica suggests that the first animals already had a complex kit of genetic tools at their disposal. Sponges harbor between 18,000 and 30,000 genes — roughly the same number as humans, fruit flies, roundworms and other animals. [Science News, 8/4/10]
Plentiful and Potential Planets: Two planet-hunting telescopes - CoRoT and Kepler - are keeping astronomers hard at work cataloging far-distant planets that orbit other stars in our galaxy. The search for distant planets is essential for astrobiologists who are hunting for habitable, Earth-like worlds beyond our solar system. [Physorg.com, 6/23/10]
World’s Most Intense X-Ray Laser Takes First Shots: The world’s most intense X-ray laser may soon be the fastest strobe-light camera ever. Two of the laser’s first experiments show the device will be able to take snapshots of single molecules in motion — without destroying them first. [Wired Science, 6/30/10]
The origin of life: putting chemistry inside a cell: In Szostak's view, interesting chemistry is easy. He also said that Darwinian evolution also makes things easy, since it's possible to take what you've got and radically improve it. So what's bugging him these days is the transition in between the two. How do you move from interesting chemistry to something that can evolve? He's doing this by trying to engineer a system that can make the transition. [Nobel Intent, 6/28/10]
Why weather != climate: the engine behind climate models: In this article I take a look at climate modeling and in particular why the comment "They can't predict the weather, therefore climate models are not good" is just plain wrong. It represents a fundamental misunderstanding of what climate modelers are trying to achieve, what is achievable and why the weather is unpredictable. [Nobel Intent, 7/9/10]
Does Your Language Shape How You Think?: The habits of mind that our culture has instilled in us from infancy shape our orientation to the world and our emotional responses to the objects we encounter, and their consequences probably go far beyond what has been experimentally demonstrated so far; they may also have a marked impact on our beliefs, values and ideologies. We may not know as yet how to measure these consequences directly or how to assess their contribution to cultural or political misunderstandings. But as a first step toward understanding one another, we can do better than pretending we all think the same. [New York Times, 8/26/10]
Stem Cell Biology and Its Complications: Stem cell biology turned out to be more complicated than they anticipated. Besides the stem cells from embryos, there are so-called adult stem cells found in all tissues but with limited potential because they can only turn into cells from their tissue of origin. And there are these newer cells made by reprogramming mature cells. [New York Times, 8/24/10]
Scientists Square Off on Evolutionary Value of Helping Relatives: For the past 46 years, biologists have used Dr. Hamilton’s theory to make sense of how animal societies evolve. They’ve even applied it to the evolution of our own species. But in the latest issue of the journal Nature, a team of prominent evolutionary biologists at Harvard try to demolish the theory. [New York Times, 8/30/10]
Think You're Operating on Free Will? Think Again: There may be few things more fundamental to human identity than the belief that people are rational individuals whose behavior is determined by conscious choices. But recently psychologists have compiled an impressive body of research that shows how deeply our decisions and behavior are influenced by unconscious thought, and how greatly those thoughts are swayed by stimuli beyond our immediate comprehension. [Time, 7/2/10]
Forget What You Know About Good Study Habits: In recent years, cognitive scientists have shown that a few simple techniques can reliably improve what matters most: how much a student learns from studying. The findings can help anyone, from a fourth grader doing long division to a retiree taking on a new language. But they directly contradict much of the common wisdom about good study habits, and they have not caught on. [New York Times, 9/6/10]
Gene networks underlie disease?: An international group of researchers have developed a novel method for identifying entire networks of genes and their association to disease, providing a more accurate picture of the genetic risks associated with specific diseases than single genes can provide. [The Scientist, 9/8/10]
Collider gets yet more exotic 'to-do' list: As if the Large Hadron Collider (LHC) didn't have enough to look for. It is already charged with hunting for the fabled Higgs boson, extra dimensions and supersymmetry, but physicists are now adding even more elaborate phenomena to its shopping list — including vanishing dimensions that could explain the accelerating expansion of the Universe. Some argue that signs of new and exotic physics could show up in the LHC far sooner than expected. [Nature News, 7/20/10]
Under Pressure: The Search for a Stress Vaccine: Chronic stress, it turns out, is an extremely dangerous condition. ... While stress doesn’t cause any single disease — in fact, the causal link between stress and ulcers has been largely disproved — it makes most diseases significantly worse. The list of ailments connected to stress is staggeringly diverse and includes everything from the common cold and lower-back pain to Alzheimer’s disease, major depressive disorder, and heart attack. [Wired Magazine, 7/28/10]
Why some memories stick: A study published in Science this week indicates that reactivating neural patterns over and over again may etch items into the memory. People find it easier to recall things if material is presented repeatedly at well-spaced intervals rather than all at once. For example, you're more likely to remember a face that you've seen on multiple occasions over a few days than one that you've seen once in one long period. One reason that a face linked to many different contexts — such as school, work and home — is easier to recognize than one that is associated with just one setting, such as a party, could be that there are multiple ways to access the memory. This idea, called the encoding variability hypothesis, was proposed by psychologists about 40 years ago. [Nature News, 9/9/10]
DNA 'Volume Knobs' May Be Associated With Obesity: When it comes to our expanding waistlines, we usually blame either diet or genes. But a new study fingers a third culprit: chemicals that attach to DNA and change its function. A survey of millions of these modifications has uncovered a handful associated with body mass index, a measure of height and weight. [Science Now, 9/15/10]
Astronomy and particle physics race to replace Standard Model: If energy issues seem to be attracting the attention of a lot of physicists, the Large Hadron Collider seems to be drawing the attention of many of the rest of them, including people in fields like cosmology, which deals with items on the opposite end of the size scale. In turn, the people working on the LHC and other particle detectors are carefully paying attention to the latest astronomy results, hoping they'll put limits on the properties and identities of the zoo of theoretical particles that need to be considered. [Nobel Intent, 7/28/10]
Sizing Up Consciousness by Its Bits: Consciousness, Dr. Tononi says, is nothing more than integrated information. Information theorists measure the amount of information in a computer file or a cellphone call in bits, and Dr. Tononi argues that we could, in theory, measure consciousness in bits as well. When we are wide awake, our consciousness contains more bits than when we are asleep. [New York Times, 9/20/10]
Translating Stories of Life Forms Etched in Stone: The Ediacaran fossils tell us that Darwin was being too generous. Our earliest animal ancestor probably had no head, tail, or sexual organs, and lay immobile on the sea floor like a door mat. [New York Times, 7/26/10]

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Hubble captures bubbles and baby stars

2010-08-10T23:19:00.000-07:00

Hubble captures bubbles and baby stars (6/22/10)

The NASA/ESA Hubble Space Telescope captures a complex network of gas clouds and star clusters within our neighbouring galaxy, the Large Magellanic Cloud. This region of energetic star birth is one of the most active in the nearby Universe.

The Large Magellanic Cloud contains many bright bubbles of glowing gas. One of the largest and most spectacular is LHA 120-N 11, from the catalogue compiled in 1956 by the late astronomer and astronaut Karl Henize. It is informally known as N11.

Close up, N11’s billowing pink clouds of glowing gas resemble a puffy swirl of fairground candyfloss. From further away, its distinctive overall shape led some observers to nickname it the Bean Nebula. The dramatic and colourful features in the nebula are the telltale signs of star birth.

N11 is a well-studied region that extends across 1000 light-years. It is the second largest star-forming region within the Large Magellanic Cloud and has produced some of the most massive stars known.

N11 – click for 2500×2458 image

More: here

What does marathon running do to an athlete's cells?

2010-08-08T19:39:00.000-07:00

If you've ever taken up running as a form of exercise, or even thought about it, there's a certain paradox that may have occurred to you. The health benefits of aerobic exercise are well-documented. (See here, for example.) In particular such exercise has been shown to reduce risks of cardiovascular disease, diabetes, and some forms of cancer. Beneficial physiological effects include reduction of high blood pressure, better control of blood sugar, and reducing blood levels of low-density lipoprotein while raising levels of high-density lipoprotein.

On the other hand, exercise necessarily increases a person's rate of metabolism, as food is processed to provide energy expended through exercise. An inevitable side-effect of metabolism is the production of reactive oxygen species (ROS) and "free radicals" that can damage DNA and other cellular constituents. This cellular damage can lead to either cancer or accelerated aging due to cell senescence and cell death.

The paradox, then, is that the health benefits of exercise do not seem to be canceled out by the side-effects of higher rates of metabolism. It's an important issue not just for humans who are trying to stay healthy, but even more important in animals like birds that may need to expend energy continuously over significant periods of time.

So what's going on here? Perhaps this research has some of the answer:

The effect of marathon on mRNA expression of anti-apoptotic and pro-apoptotic proteins and sirtuins family in male recreational long-distance runners

Background

A large body of evidence shows that a single bout of strenuous exercise induces oxidative stress in circulating human lymphocytes leading to lipid peroxidation, DNA damage, mitochondrial perturbations, and protein oxidation.

In our research, we investigated the effect of physical load on the extent of apoptosis in primary cells derived from blood samples of sixteen healthy amateur runners after marathon (a.m.).

Results

Blood samples were collected from ten healthy amateur runners peripheral blood mononuclear cells (PBMCs) were isolated from whole blood and bcl-2, bax, heat shock protein (HSP)70, Cu-Zn superoxide dismutase (SOD), Mn-SOD, inducible nitric oxide synthase (i-NOS), SIRT1, SIRT3 and SIRT4 (Sirtuins) RNA levels were determined by Northern Blot analysis. Strenuous physical load significantly increased HSP70, HSP32, Mn-SOD, Cu-Zn SOD, iNOS, GADD45, bcl-2, forkhead box O (FOXO3A) and SIRT1 expression after the marathon, while decreasing bax, SIRT3 and SIRT4 expression (P < 0.0001).

Conclusion

These data suggest that the physiological load imposed in amateur runners during marathon attenuates the extent of apoptosis and may interfere with sirtuin expression.

There are two main findings here, related to apoptosis and sirtuin expression. Let's take them in order.

Apoptosis is a form of programmed cell death that has several purposes. The invocation of a cell's apopotosis program isn't necessarily an indication that something is wrong. For example, it occurs normally during embryonic development. Early in the development process embryos of all tetrapods have tissues between what will become the fingers and toes of their hands and feet. But since animals that have left an aquatic environment are usually better off without this extra tissue, evolution has led to signals at a certain stage of embryonic development that cause apoptosis in the cells of the relevant tissue. This is an example of what's known as the "extrinsic" apoptotic pathway.

But for our present purposes there's a second pathway – the "intrinsic" pathway – which is used whenever a cell either detects internal damage (usually to its DNA) or some stressful condition, such as an excessive level of reactive oxygen species. A ROS is a chemically-reactive molecule containing oxygen, including what are sometimes called "free radicals".

This condition of excess ROS is called oxidative stress. It can occur for various reasons, including exposure to high levels of heat or ultraviolet radiation – or abnormally rapid cell metabolism due to vigorous exercise. Cells recognize the condition of oxidative stress indirectly though signaling involving various other molecules that are produced in response to particular ROS molecules. Among such indicators are proteins called heat shock proteins. Two members of this family that were measured in the research under discussion were HSP70 and HSP32.

Signals of oxidative stress trigger the second, "intrinsic" apoptotic pathway, which involves a cell's energy-producing organelles, the mitochondria. The main players in the intrinsic pathway are proteins called, generically, "caspases" – short for "cysteine-rich aspartate proteases". Caspases are enzymes that cleave proteins at aspartate units. (Cysteine and aspartate are two of the 21 amino acids that normally make up proteins.)

Caspases are fairly active enzymes, so they don't ordinarily occur at significant concentrations within cells. Instead, they are produced when needed from other protein enzymes called procaspases. One of these, procaspase-9 is found normally within mitochondria, along with another protein, cytochrome c. Most of the time these proteins are confined within the mitochondria. However, under certain conditions some channels in a mitochondrion's membrane can open and allow the release of procaspase-9 and cytochrome c. Once these proteins enter the cytosol (cell fluid) outside a mitochondrion, they can team up with another protein (Apaf-1: "apoptotic protease activating factor 1") to convert the procaspase-9 into the caspase known as caspase-9. The latter is an active enzyme that leads to the production of other caspases, with cell apoptosis as the eventual result.

Since a cell does not want to have apoptosis going on normally, the process must be tightly regulated. This is done (partly) by another pair of proteins, Bcl-2 and Bax. These two proteins have structural similarities and are considered to be in the same family, the Bcl-2 family. They are always present in the cytosol, and the relative concentration between Bcl-2 and Bax is what controls whether mitochondrial membrane channels will allow release of procaspase-9 and cytochrome c. If the ratio favors Bcl-2, the channels are essentially closed – the normal case – but if the ratio favors Bax, the channels open... and apoptosis may follow.

The present research measured the levels of certain proteins in 10 individuals before and after a marathon run. (The measurement was done indirectly by measuring levels of mRNA transcripts of the associated genes.) A key finding was that the ratio of Bcl-2 to Bax shifted in favor of Bcl-2 from the before to the after measurement. In other words, there was an anti-apoptotic effect, which countered the pro-apoptotic effects of ROS molecules produced by vigorous exercise. Although ROS levels were not measured (since there was no corresponding mRNA), levels of superoxide dismutase (SOD) antioxidants (Mn-SOD and Cu-Zn-SOD) increased after the marathons, reflecting ROS production.

Analysis of the results indicates that apoptosis actually was inhibited, though less in some experimental subjects than others. An increase in levels of procaspase-9 was not observed. Further, in 7 of the 10 experimental subjects, there was little evidence of DNA fragmentation (a consequence of apoptosis). In the other 3 subjects, there was some evidence of DNA fragmentation, but also smaller changes in the Bcl-2 to Bax ratios.

Most interestingly, there was a significant positive correlation in after marathon measurements between levels of Bcl-2 and both HSP70 and HSP32. This suggests that the expected increases of HSP70 and HSP32 may play some part in increased Bcl-2 levels. There was also a positive correlation post-marathon between HSP70 and Mn-SOD levels.

These findings, especially given the small sample size, certainly aren't conclusive. But, as the paper says, "Here, we have found a significant relationship between HSP70 and bcl-2 RNA ... following marathon, but the underlying cellular and molecular mechanisms involved in this [sic] exercise induced adaptations in apoptosis and HSP70 are unknown and require further investigation."

Expression of the sirtuins SIRT1, SIRT3, and SIRT4 pre- and post-marathon were also measured. (We've discussed the sirtuins on a number of occasions.) There's an extensive history of research on SIRT1, concerning its connections with such things as cellular metabolism, cell survival under stress, and antioxidant activity. Research on other sirtuins like SIRT3 and SIRT4 is less extensive. However, members of this family have various things in common. All are enzymes. SIRT1 and SIRT3 are histone deacetylases (HDACs), so have epigenetic roles in affecting gene expression. SIRT3 and SIRT4 occur in mitochondria.

Although it's possible to make various speculations about how sirtuins could be involved with apoptosis and metabolic consequences of exercise, not all that much is known about specific molecular mechanisms. Nevertheless, it's interesting that the present research does show an effect of strenuous exercise on SIRT1, SIRT3, and SIRT4 expression. The paper notes that "the RNA contents of SIRT1 increased substantially in the group after marathon.... On the other hand, the RNA contents of SIRT3 and SIRT4 decreased in the group after marathon."

Further research into these connections could be very interesting.

Marfe, G., Tafani, M., Pucci, B., Di Stefano, C., Indelicato, M., Andreoli, A., Russo, M., Sinibaldi-Salimei, P., & Manzi, V. (2010). The effect of marathon on mRNA expression of anti-apoptotic and pro-apoptotic proteins and sirtuins family in male recreational long-distance runners BMC Physiology, 10 (1) DOI: 10.1186/1472-6793-10-7

Further reading:

Running a marathon halts cellular suicide (5/11/10)

Articles related to sirtuins:

Sirtuin proteins (11/16/07)

The discovery of sirtuins, part 1 (11/17/07)

The discovery of sirtuins, part 2 (11/20/07)

Sirtuin news (1/21/08)

SIRT1 and cancer (10/26/08)

VISTA Views the Sculptor Galaxy

2010-08-01T18:47:00.000-07:00

VISTA Views the Sculptor Galaxy (6/16/10)

A spectacular new image of the Sculptor Galaxy (NGC 253) has been taken with the ESO VISTA telescope at the Paranal Observatory in Chile as part of one of its first major observational campaigns. By observing in infrared light VISTA’s view is less affected by dust and reveals a myriad of cooler stars as well as a prominent bar of stars across the central region. The VISTA image provides much new information on the history and development of the galaxy.

The Sculptor Galaxy (NGC 253) lies in the constellation of the same name and is one of the brightest galaxies in the sky. It is prominent enough to be seen with good binoculars and was discovered by Caroline Herschel from England in 1783. NGC 253 is a spiral galaxy that lies about 13 million light-years away. It is the brightest member of a small collection of galaxies called the Sculptor Group, one of the closest such groupings to our own Local Group of galaxies. Part of its visual prominence comes from its status as a starburst galaxy, one in the throes of rapid star formation. NGC 253 is also very dusty, which obscures the view of many parts of the galaxy (eso0902). Seen from Earth, the galaxy is almost edge on, with the spiral arms clearly visible in the outer parts, along with a bright core at its centre.

NGC 253 – click for 1600×1200 image

I write like Cory Doctorow

2010-08-01T13:50:00.000-07:00

I write like
Cory Doctorow

I Write Like by Mémoires, Mac journal software. Analyze your writing!

Interesting. I know who Cory is, and have even heard him speak, but haven't ever read something he's written.

So just for fun I analyzed another passage and got:

I write like
George Orwell

I Write Like by Mémoires, Mac journal software. Analyze your writing!

I assume this site refers mostly to top authors... I mean who'd like to be told "I write like Edward George Bulwer-Lytton"?

To test that hypothesis, I plugged in some of the worst writing I could think of (not mentioning any names) and out popped... David Foster Wallace. I put a Wikipedia link on that since I didn't recognize the name at first. Wikipedia refreshed my memory. I've never read anything by Mr. Wallace either, but given the person who was said to write like him, I don't think I'll be in any rush to check him out...

Update:

Another name I should check out just occurred to me – that of a person who happens to be a well-known and much celebrated contemporary science writer, but whose prose I don't much care for either and got... David Foster Wallace. Hmm. I see a pattern here and am even more convinced to give Mr. Wallace's works a pass...

A New Look into the Whirlpool

2010-07-31T03:10:00.000-07:00

A New Look into the Whirlpool

Galaxy M51 was discovered by Charles Messier in 1773, but its outstanding spiral structure was first perceived by William Parsons (Earl of Rosse) in 1845, using his huge reflecting telescope, the Leviathan of Parsonstown. A large telescope is needed to see its intricate shape, but even small amateur telescopes reveal that this galaxy is not isolated, but has a small companion, the dwarf irregular galaxy NGC 5195.

Now it is clear that these two stellar systems are colliding and that the outstanding spiral shape of M51 is due, mainly, to the tidal forces unleashed during this process. Just by chance, we see the disk of M51 face on from Earth, what allows studying it in detail. At a distance of 23 millions of light-years, the apparent dimensions of M51 mean that that galaxy has to be quite similar to our own, yet somewhat smaller.

M51 and its companion are performing a cosmic dance that, during the last 500 million years has made NGC 5195 pass twice through the disk of M51. Now, the small galaxy is located slightly behind the disc of the Whirlpool, and moving away from us.

M51 and NGC 5195 – Click for 1600×1583 image

More: here

Selected readings 7/25/10

2010-07-25T17:51:00.000-07:00

The Muon Guys: On the Hunt for New Physics: The experiment will search for a phenomenon so incredibly rare that, according to the Standard Model of physics, humans could never build a machine sensitive enough to actually see it. Which is exactly why scientists want to build this experiment. Mu2e is on the hunt for new physics. [Symmetry Magazine, 6/1/10]
SLAC’s new X-ray laser peels and cores atoms: The first published scientific results from the world’s most powerful hard X-ray laser, located at the Department of Energy’s SLAC National Accelerator Laboratory, show its unique ability to control the behaviors of individual electrons within simple atoms and molecules by stripping them away, one by one—in some cases creating hollow atoms. [Symmetry Breaking, 7/2/10]
Antiaging protein also boosts learning and memory: Aging and wisdom are supposed to go together, but it turns out that a molecule that prevents one may actually play a role in the other. Researchers have discovered a new role for the famous antiaging protein SIRT1. It not only fends off aging, but also aids in learning and memory, a new study published online July 11 in Nature shows. [Science News, 7/12/10]
Galaxies weigh in on neutrinos: Neutrinos are infamously lightweight particles that are near impossible to detect, let alone place on a scale. Yet our most basic model for understanding the symmetries of matter and particles rests on an accurate measure of the neutrino masses. Over the past decade, observational cosmology has taken a leading position in providing an upper bound on these masses. Now, in a paper appearing in Physical Review Letters, Shaun Thomas, Filipe Abdalla, and Ofer Lahav at University College London in the UK predict that the total neutrino mass, summed over the three neutrino families, is smaller than 0.28 eV—the tightest upper bound yet. Their prediction is based on a new mapping of the distribution of density of surrounding galaxies. [Physics, 7/12/10]
Neutrino quick-change artist caught in the act: Physicists have for the first time found direct evidence that a neutrino, a ghostly elementary particle that barely interacts with matter, morphs from one type into another. The finding provides additional support for the notion that neutrinos have mass, a property that requires an explanation beyond the realm of the standard model of particle physics. [Science News, 6/1/10]
Magic quantum wand does not vanish hard math: They conclude that NP-complete problems are just as hard on an adiabatic quantum computer as on a classical computer. And, since earlier work showed the equivalence between different variants of quantum computers, that pretty much shuts down the possibility of any quantum computer helping with NP-complete problems. [Nobel Intent, 6/3/10]
An unpaleontological lament for lost molecules and shattered cells and the cruelty of time: These were almost certainly colonial organisms that took advantage of the higher concentration of oxygen to build denser mats on top of the sea floor. They probably weren't true multi-cellular organisms; they were a step up from a colony of bacteria that you might see growing on a petri dish, but with additional molecular features that permitted greater coordination and the development of more elaborate spatial patterning. [Pharyngula, 7/15/10]
Cosmology forum: Is dark energy really a mystery?: The Universe is expanding. And the expansion seems to be speeding up. To account for that acceleration, a mysterious factor, 'dark energy', is often invoked. A contrary opinion — that this factor isn't at all mysterious — is here given voice, along with counter-arguments against that view. [Nature, 7/14/10]
How to read a genome-wide association study: As any avid follower of genomics or medical genetics knows, genome-wide association studies (GWAS) have been the dominant tool used by complex disease genetics researchers in the last five years. There’s a very active debate in the field about whether GWAS have revolutionized our understanding of disease genetics or whether they were a waste of money for little tangible gain. [Genomes Unzipped, 7/18/10]
Brain's bubble wrap may be lots more: They have long been dismissed as the brain’s Bubble Wrap, packing material to protect precious cells that do the real work of the mind. But glial cells — the name literally means “glue’’ — are now being radically recast as neuroscientists explore the role they play in disease and challenge longstanding notions about how the brain works. [Boston Globe, 5/31/10]
Collider gets yet more exotic 'to-do' list: As if the Large Hadron Collider (LHC) didn't have enough to look for. It is already charged with hunting for the fabled Higgs boson, extra dimensions and supersymmetry, but physicists are now adding even more elaborate phenomena to its shopping list — including vanishing dimensions that could explain the accelerating expansion of the Universe. Some argue that signs of new and exotic physics could show up in the LHC far sooner than expected. [Nature News, 7/20/10]
Shock and Age: The accumulation of misfolded protein marks the accrual of years as the body ages. Could heat shock proteins be used to reduce the effects of aging and diminish the risk of disease by untangling improperly folded proteins? [The Scientist, 6/1/10]
Quantum mechanics flummoxes physicists again: Weihs and colleagues aimed a source of single photons (which, like electrons, exhibit wave–particle duality) at a mask containing various open and closed combinations of three slits. The authors fired photons repeatedly through the mask, while building a probability distribution of photons arriving on a detector beyond it. From the probabilities of each combination, they could calculate a crucial interference term, which would highlight any three-path interference. [Nature News, 7/22/10]

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Quasars in the very early universe

2010-07-17T20:35:00.000-07:00

Quasars are powered by the gravitational (potential) energy of their central supermassive black holes. However, their distinctive features – their extremely high luminosity in particular – are very dependent on characteristics of matter close to the black hole.

Most supermassive black holes (SMBH), including those at the centers of the Milky Way and our close neighbor M31 (Andromeda), are responsible for fairly small amounts of radiation in any part of the electromagnetic spectrum. This is generally because the radiation of a quasar is produced mainly by the infall of matter during a relatively brief period of the object's life – a few percent of the total, i. e. a few hundred million years. Once the nearby matter is used up, the lights go out.

(For earlier articles on quasars, see here.)

In a quasar, where matter in significant quantities is still being accreted, most of the radiation originates in a central "accretion disk" close to the black hole. The radiation is thermal ("black body") produced by very hot gas consisting mostly of hydrogen and helium. This radiation covers the spectrum from infrared to X-rays. Since quasars are so bright, they can be seen individually at high redshifts – z≥6, which is not true of ordinary galaxies. That corresponds to times within a billion years of the big bang. At z≈6 photon wavelengths are stretched by a factor of 7, so what we actually see is not the rest-frame spectrum, but a considerably red-shifted version of it.

If r_s is the Schwarzschild radius, then the accretion disk extends from a radius of about 3 times r_s outward to a few hundred times r_s. To give a sense of the scale, a largish SMBH has a mass of a billion solar masses. So for such an object r_s is about the radius of the orbit of Uranus, by a simple calculation given here.

Quasars and active galaxies (i. e. just smaller versions of the same thing) have been intensively studied for several decades. In that time, a fairly clear picture has emerged of how matter is distributed further out from the accretion disk. The most prominent feature of this region is a thick (compared to the accretion disk) torus-shaped ring of cooler gas and dust. The "dust" consists of very small particles composed of various elements heavier than helium. Electromagnetic radiation from the torus is mostly in the infrared part of the spectrum (rest frame), and is produced by re-emission (at lower energies) of higher energy photons from the accretion disk.

The shape of this region is not strictly a torus, since it's considerably flattened, especially at higher distances from the center, but it's referred to as a torus for simplicity. The outer limits of quasar tori are hard to determine, but probably extend hundreds of light years from the center. However, the inner parts are thick enough that unless we are seeing the quasar almost face-on (i. e., along the symmetry axis of the accretion disk and torus), we cannot clearly see the accretion disk itself, because it's obscured by the dust in the torus.

One interesting thing about quasars is that as far as we can tell (until quite recently), their characteristics are very similar no matter how distant they are. Although the present-day universe is quite different in many respects from what it was a billion years after the big bang, quasars seem hardly different at all.

Research published just this year is starting to change this story:

Dust-free quasars in the early Universe

The most distant quasars known, at redshifts z ≈ 6, generally have properties indistinguishable from those of lower-redshift quasars in the rest-frame ultraviolet/optical and X-ray bands. This puzzling result suggests that these distant quasars are evolved objects even though the Universe was only seven per cent of its current age at these redshifts. Recently one z ≈ 6 quasar was shown not to have any detectable emission from hot dust, but it was unclear whether that indicated different hot-dust properties at high redshift or if it is simply an outlier. Here we report the discovery of a second quasar without hot-dust emission in a sample of 21 z ≈ 6 quasars. Such apparently hot-dust-free quasars have no counterparts at low redshift. Moreover, we demonstrate that the hot-dust abundance in the 21 quasars builds up in tandem with the growth of the central black hole, whereas at low redshift it is almost independent of the black hole mass. Thus z ≈ 6 quasars are indeed at an early evolutionary stage, with rapid mass accretion and dust formation. The two hot-dust-free quasars are likely to be first-generation quasars born in dust-free environments and are too young to have formed a detectable amount of hot dust around them.

Some things in these results are actually more interesting than that a few very early quasars are different from all other quasars. In the very early universe at z>6, less intergalactic dust is to be expected. This is because the dust – which is composed of elements heavier than helium – is (by conventional accounts) produced mostly in stars. It is expelled from stars only either gradually, as the star evolves, or suddenly in the rare case of supernova explosions.

We still don't know very precisely when the very first stars formed (see here), but that probably happened only a few hundred million years after the big bang. Since the very first stars must have consisted almost entirely of hydrogen and helium, star-formation models indicate they should have been much more massive than typical later stars, and they should have expoded as supernovae after only a few tens of millions of years. As heavier elements gradually accumulated in the universe, stars of a more modern sort, initially containing small amounts of heavier elements, began to form. These later stars were small enough so that most never ended as supernovae, but they continued to manufacture and expel heavier elements – and hence dust.

Observations of very early quasars therefore tell us a little about the pace of this process. We now know, for example, of at least two quasars that formed so early that they do not have any dust around them that we can observe. The evidence for this is that emissions of these two quasars at rest-frame wavelengths from ultraviolet to very near infrared appear normal. Dust, however, should also produce rest-frame emissions in farther infrared – and that's not seen in these two examples, although it is in all other of the sampled z≈6 quasars.

One other feature of z≈6 quasars is particularly interesting. The mass of a quasar can be estimated from total luminosity and certain spectral features. In all z≈6 quasars that do have evidence of dust, the amount of dust is roughly proportional to the SMBH mass. However, in low-redshift quasars, dust abundance is almost uncorrelated with mass. The implication, then, is that in their youngest stages, but not later, quasars accumulate dust at about the same rate as SMBH mass. And indeed, the two quasars without apparent dust also have the smallest SMBH mass of any in the sample, about 2 to 3×10⁸ M_⊙.

This raises another interesting, unanswered question. Just where does this dust come from? It's generally thought that in the present universe most of the existing dust originated from ordinary stars. However, at z≈6 most stars would be less than 500 million years old, and it's not at all clear this would have allowed enough time for the production of sufficient dust. Supernovae are another possibility, but even in the early universe we don't know whether they would have been common enough.

Further, the existence of elements heavier than helium is necessary but not sufficient to produce dust. Most models assume also a proper combination of relatively low temperature (<2000 K) and high density is also required for dust to form. But a theoretical study (astro-ph/0202002) suggests that dust could actually form in the vicinity of a quasar itself. Some combination of all these possibilities may be the answer, but a lot more research will probably be needed to clear this up.

Every time we learn something new, it seems, we also find new questions.

Jiang, L., Fan, X., Brandt, W., Carilli, C., Egami, E., Hines, D., Kurk, J., Richards, G., Shen, Y., Strauss, M., Vestergaard, M., & Walter, F. (2010). Dust-free quasars in the early Universe Nature, 464 (7287), 380-383 DOI: 10.1038/nature08877

Further reading:

NASA's Spitzer Unearths Primitive Black Holes (3/17/10)

Quasar Dust in the Early Universe (3/26/10)

Primordial Black Holes Formed Just After Big Bang (3/17/10)

First generation of quasars (3/17/10)

Related articles:

Where the action is in black hole jets (5/12/10)

Active galaxies and supermassive black hole jets (4/25/10)

Selected readings 7/13/10

2010-07-13T23:59:00.000-07:00

A Decade Later, Genetic Map Yields Few New Cures: Ten years after President Bill Clinton announced that the first draft of the human genome was complete, medicine has yet to see any large part of the promised benefits. For biologists, the genome has yielded one insightful surprise after another. But the primary goal of the $3 billion Human Genome Project — to ferret out the genetic roots of common diseases like cancer and Alzheimer’s and then generate treatments — remains largely elusive. Indeed, after 10 years of effort, geneticists are almost back to square one in knowing where to look for the roots of common disease. [New York Times, 6/12/10]
How Our Brains Make Memories: His ideas are unconventional within neuroscience, and they have caused researchers to reconsider some of their most basic assumptions about how memory works. In short, Nader believes that the very act of remembering can change our memories. [Smithsonian Magazine, 4/19/10]
Writing Circuits on Graphene: Graphene, an atom-thick carbon sheet, is a promising replacement for silicon in electronic circuits, since it transports electrons much faster. IBM researchers have already made transistors, the building blocks of electronic circuits, with graphene that work 10 times faster than their silicon counterparts. [Technology Review, 6/15/10]
Rare Gene Glitch a Clue to Genomics Mystery: Common diseases have largely resisted genomic analysis, leaving scientists unable to explain genetic underpinnings of diseases that clearly have a hereditary component. These analyses have focused on mutations that are relatively widespread and easy to see. It took new tools to notice mutations like those just found in the SIAE gene, which cause immune cells to go haywire during autoimmune disease. They were detected by ultra high-resolution analysis of a sort rarely used in genomics. [Wired, 6/16/10]
Test Supports Universal Common Ancestor for All Life: One researcher put the basic biological assumption of a single common ancestor to the test--and found that advanced genetic analysis and sophisticated statistics back up Darwin's age-old proposition. [Scientific American, 5/13/10]
Frozen methane, from the gulf oil spill to climate change: At the conditions in which they form, methane is a gas, water a liquid. Somehow, they come together to form a solid. The key to understanding why is the small size and nonpolar (hydrophobic) nature of methane. [Nobel Intent, 5/11/10]
New evidence for quantum Darwinism found in quantum dots: Physicists have found new evidence that supports the theory of quantum Darwinism, the idea that the transition from the quantum to the classical world occurs due to a quantum form of natural selection. By explaining how the classical world emerges from the quantum world, quantum Darwinism could shed light on one of the most challenging questions in physics of the past century. [Physorg.com, 5/10/10]
I.B.M.'s Supercomputer to Challenge 'Jeopardy!' Champions: For the last three years, I.B.M. scientists have been developing what they expect will be the world’s most advanced “question answering” machine, able to understand a question posed in everyday human elocution — “natural language,” as computer scientists call it — and respond with a precise, factual answer. In other words, it must do more than what search engines like Google and Bing do, which is merely point to a document where you might find the answer. It has to pluck out the correct answer itself. [New York Times, 6/14/10]
New Nicaraguan sign language shows how language affects thought: NSL is not a direct translation of Spanish – it is a language in its own right, complete with its own grammar and vocabulary. Its child inventors created it naturally by combining and adding to gestures that they had used at home. Gradually, the language became more regular, more complex and faster. Ever since, NSL has been a goldmine for scientists, providing an unparalleled opportunity to study the emergence of a new language. And in a new study led by Jennie Pyers from Wellesley College, it even tells us how language shapes our thought. [Not Exactly Rocket Science, 6/22/10]
Hunt for genetic causes of diseases narrows targets: The falling cost of genome sequencing has kicked off a new phase in the search for the genetic underpinnings of complex diseases such as asthma, diabetes and autism. [Nature News, 5/18/10]
Researchers tweak fMRIs to map the brain's wiring schematic: Researchers were able to limit the firing of nerve cells to a specific individual type, and show that these triggered normal-looking fMRI signals in rats. Not only does this place fMRI on a firmer empirical footing, the technique allowed the researchers to track networks of connected nerves within the brain. [Nobel Intent, 5/17/10]
Fermi's Tevatron finds another bias against antimatter: Over the last couple of decades, a few cases of what are called C-P violations have been identified. These are cases where a particle decay that should, in theory, produce equal amounts of antimatter and matter, doesn't. These few instances, however, don't occur with sufficient frequency to explain why the Universe has its current abundance of regular matter. That has kept physicists looking and, this morning, Fermilab announced that research performed in its Tevatron accelerator has provided strong evidence for another C-P violation. [Nobel Intent, 5/18/10]
Man-Made Genetic Instructions Yield Living Cells for the First Time: The first microbe to live entirely by genetic code synthesized by humans has started proliferating at a lab in the J. Craig Venter Institute (JCVI). Venter and his colleagues used a synthetic genome—the genetic instruction set for life—to build and operate a new, synthetic strain of Mycoplasma mycoides bacteria. [Scientific American, 5/20/10]
Synthetic genome resets biotech goals: Synthetic biology is a field with an audacious but ultimately utilitarian goal: to redesign the building blocks of life to serve the needs of humanity. It is also an endeavour that challenges clear-cut definitions of natural versus artificial life. [Nature News, 5/26/10]
Primordial Gravitational Waves Provide a Test of Cosmological Theories: Ripples in the fabric of spacetime could someday provide observational evidence for the goings-on in the earliest instants of the universe, revealing high-energy processes that currently remain opaque to even the largest particle colliders. [Scientific American, 5/21/10]
Neutrino experiments sow seeds of possible revolution: Neutrinos are the big nothings of subatomic physics. Nearly massless and lacking an electric charge, these ghostly particles interact so weakly with other types of matter that more than 50 trillion of them pass unimpeded through a person’s body each second. Yet recent preliminary findings from two experiments hint that neutrinos may be opening a window on a hidden world of subatomic particles and forces. [Science News, 6/25/10]
X-Ray Laser Resurrects a Laboratory No Longer in the Vanguard: In the first experiments conducted at the SLAC National Accelerator Laboratory in Menlo Park, Calif., since its outdated particle accelerator was converted into the world's brightest X-ray laser, scientists managed to create what they called hollow atoms, giving just a preview of the kind of science expected to be done there. [New York Times, 7/5/10]
SETI Redux: Joining the Galactic Club: David Schwartzman, a biogeochemist at Howard University in Washington D.C., explains why he thinks the aliens are out there, despite the fact that the search for extraterrestrial intelligence (SETI) has only found silence. He also outlines what we need to do for planet Earth to be initiated into the Galactic Club. [Physorg.com, 5/24/10]
Dark Matter May Be Building Up Inside the Sun: The sun could be a net for dark matter, a new study suggests. If dark matter happens to take a certain specific form, it could build up in our nearest star and alter how heat moves inside it in a way that would be observable from Earth. [Wired, 7/9/10]

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Starburst Cluster Shows Celestial Fireworks

2010-07-12T22:22:00.000-07:00

Starburst Cluster Shows Celestial Fireworks (7/6/10)

Like a July 4 fireworks display, a young, glittering collection of stars looks like an aerial burst. The cluster is surrounded by clouds of interstellar gas and dust—the raw material for new star formation. The nebula, located 20,000 light-years away in the constellation Carina, contains a central cluster of huge, hot stars, called NGC 3603.

This environment is not as peaceful as it looks. Ultraviolet radiation and violent stellar winds have blown out an enormous cavity in the gas and dust enveloping the cluster, providing an unobstructed view of the cluster.

Most of the stars in the cluster were born around the same time but differ in size, mass, temperature, and color. The course of a star's life is determined by its mass, so a cluster of a given age will contain stars in various stages of their lives, giving an opportunity for detailed analyses of stellar life cycles. NGC 3603 also contains some of the most massive stars known. These huge stars live fast and die young, burning through their hydrogen fuel quickly and ultimately ending their lives in supernova explosions.

NGC 3603 – click for 1000×891 image

More: here, here, here, here, here, here, here, here, here, here, here, here

Starburst Galaxy NGC 1313

2010-07-07T02:21:00.000-07:00

Starburst Galaxy NGC 1313 (5/24/10)

The starburst galaxy NGC 1313 is a stellar incubator delivering stars on a scale rarely seen in a single galaxy of its size. Now a striking new Gemini Observatory image reveals the multitudes of glowing gas clouds in this galaxy’s arms. These colorful clouds are the tell-tale sign of star-formation in this prolific star factory.

Because the clouds of gas in stellar nurseries emit light from ionized gas they shine brightly in very specific colors (or wavelengths) so narrow-band filters were used on the Gemini Multi-Object Spectrograph on the Gemini South telescope in Chile to capture the colorful galactic lightscape. The unprecedented detail and clarity of the image reveals myriad bubbles, shock fronts, star clusters, and sites where massive stars are being born.

NGC 1313 – click for 1000×747 image

More: here

Clear New View of a Classic Spiral

2010-07-01T00:49:00.000-07:00

Clear New View of a Classic Spiral (5/19/10)

The galaxy Messier 83 is located about 15 million light-years away in the constellation of Hydra (the Sea Serpent). It spans over 40 000 light-years, only 40 percent the size of the Milky Way, but in many ways is quite similar to our home galaxy, both in its spiral shape and the presence of a bar of stars across its centre. Messier 83 is famous among astronomers for its many supernovae: vast explosions that end the lives of some stars. Over the last century, six supernovae have been observed in Messier 83 — a record number that is matched by only one other galaxy. Even without supernovae, Messier 83 is one of the brightest nearby galaxies, visible using just binoculars.

Messier 83 has been observed in the infrared part of the spectrum using HAWK-I, a powerful camera on ESO’s Very Large Telescope (VLT). When viewed in infrared light most of the obscuring dust that hides much of Messier 83 becomes transparent. The brightly lit gas around hot young stars in the spiral arms is also less prominent in infrared pictures. As a result much more of the structure of the galaxy and the vast hordes of its constituent stars can be seen. This clear view is important for astronomers looking for clusters of young stars, especially those hidden in dusty regions of the galaxy.

M83 – click for 1600×1200 image

Another view of M83: here

More: here

Hubble captures bubbles and baby stars

2010-06-30T21:55:00.000-07:00

Hubble captures bubbles and baby stars (6/22/10)

The NASA/ESA Hubble Space Telescope captures a complex network of gas clouds and star clusters within our neighbouring galaxy, the Large Magellanic Cloud. This region of energetic star birth is one of the most active in the nearby Universe.

The Large Magellanic Cloud contains many bright bubbles of glowing gas. One of the largest and most spectacular is LHA 120-N 11, from the catalogue compiled in 1956 by the late astronomer and astronaut Karl Henize. It is informally known as N11. ...

N11 is a well-studied region that extends across 1000 light-years. It is the second largest star-forming region within the Large Magellanic Cloud and has produced some of the most massive stars known.

LHA 120-N 11 – click for 2500×2458 image

More: here

Creativity and mental illness

2010-06-27T21:27:00.000-07:00

The association between creativity and mental illness is sort of a cliché – but that doesn't mean there's nothing to it. Standard examples given include Vincent van Gogh, Robert Lowell, and John Nash.

There has been a rather large amount of research into the connection, and a large number of biographical accounts of famous creative people who also suffered from mental illness. But the neurobiological details are emerging only slowly. After all, our understanding of the biological roots of either creativity or mental illness remains fairly rudimentary.

However, one recent study does add some tantalizing clues.

Thinking Outside a Less Intact Box: Thalamic Dopamine D2 Receptor Densities Are Negatively Related to Psychometric Creativity in Healthy Individuals

Several lines of evidence support that dopaminergic neurotransmission plays a role in creative thought and behavior. Here, we investigated the relationship between creative ability and dopamine D2 receptor expression in healthy individuals, with a focus on regions where aberrations in dopaminergic function have previously been associated with psychotic symptoms and a genetic liability to schizophrenia. Scores on divergent thinking tests (Inventiveness battery, Berliner Intelligenz Struktur Test) were correlated with regional D2 receptor densities, as measured by Positron Emission Tomography, and the radioligands [¹¹C]raclopride and [¹¹C]FLB 457. The results show a negative correlation between divergent thinking scores and D2 density in the thalamus, also when controlling for age and general cognitive ability. Hence, the results demonstrate that the D2 receptor system, and specifically thalamic function, is important for creative performance, and may be one crucial link between creativity and psychopathology. We suggest that decreased D2 receptor densities in the thalamus lower thalamic gating thresholds, thus increasing thalamocortical information flow. In healthy individuals, who do not suffer from the detrimental effects of psychiatric disease, this may increase performance on divergent thinking tests. In combination with the cognitive functions of higher order cortical networks, this could constitute a basis for the generative and selective processes that underlie real life creativity.

Executive summary: There is a correlation between performance on a part of a common psychological test for creativity and a certain property of neurons in a brain structure called the thalamus. The association with mental illness, specifically schizophrenia, is that the same neural abnormality in the same part of the brain has also been found to correlate with various symptoms of schizophrenia.

Let's look at creativity first. It's often defined, to quote from the research paper, as "the ability to produce work that is at the same time novel and meaningful, as opposed to trivial or bizarre". A creative work should be original and unexpected, but it should also be more than just randomly different from the ordinary. It should also impress us as insightful or solve a difficult problem.

So there are several abilities a creative person should possess. They don't necessarily correlate with each other, but all or most should be present for "true" creativity. A creative artist, for instance, should be inventive and original, but also have good artistic skills. As far as the present research is concerned, we're dealing just with the aspect of creativity that comprises novelty and originality.

The psychological test used in this research is called the "Berliner Intelligenz Struktur Test". It's a general intelligence test, and it consists of several parts. One part is the "Inventiveness battery", and the specific ability that measures is called "divergent thinking".

Even within the divergent thinking component, several characteristics can be distinguished. The test may ask, for example, to think of as many reasonable uses as possible for an object like a brick. The characteristics that might be observed include:

Fluency–the number of valid responses; Originality–how frequent the participant's responses were among the responses of the rest of the sample; Flexibility–the number of semantic categories produced; Switching–the number of shifts between semantic categories; and Elaboration–how extensive each response is (if the task involves producing more than single words).

To do well on this test, a subject must be able to quickly produce valid responses that are unobvious and diverse in nature, not just variations on a few themes.

Previous research had established that divergent thinking is influenced by the "dopaminergic" neural system, i. e., neurons whose primary neurotransmitter is dopamine. Specifically, there is a correlation between divergent thinking (as measured by the test just described) and certain variants of the dopamine D2 receptor. The present research further narrows down the relationship.

We've discussed dopamine before (list). It is involved in quite an impressive number and diversity of psychological phenomena, including appetite, addiction, risk-taking, memory, and trust. Some abnormalities of the dopaminergic system are also implicated in pathologies such as ADHD, Parkinson's disease, depression, and schizophrenia (dum-da-dum-dum).

Indeed, because dopamine is involved in so many functions, therapies for certain dopamine-related disorders can cause side effects in seemingly unrelated areas. For example, Parkinson's disease results from insufficient dopamine activity, but treatments that raise dopamine levels can cause other problems, such as pathological gambling, compulsive shopping, binge eating and other impulse control disorders. (Ref.: here.)

The reason that dopaminergic neuron abnormalities have such diverse effects is that dopaminergic neurons are common in a number of specialized areas of the brain. A dopamine abnormality will therefore affect whatever function such an area is involved in.

As far as divergent thinking is concerned, there are two brain areas of particular interest: the striatum and thalamus. Many neurons in both regions have D2 receptors. And interestingly enough, these regions are also linked with schizophrenia. As the research paper notes,

[N]etworks relevant to divergent thinking, i.e. structures and processes in associative corticostriatal-thalamocortical loops overlap to a great extent with regions and networks affected in schizophrenia and bipolar disorder. Furthermore, dopamine is known to influence processing in these networks and alterations in dopaminergic function and activity of D2 receptors have been linked to both positive and negative psychotic symptoms. Two regions appear to be of particular interest in this context: the thalamus and the striatum. Several studies have shown thalamic D2BP to be reduced in drug-naïve schizophrenia patients. Moreover, D2BP in subregions of the thalamus was found to be negatively related to total symptoms, general symptoms, positive symptoms, hostility and suspiciousness as well as grandiosity.

(D2BP refers to D2 "binding potential", which depends on the number density of D2 receptors and their ability to bind dopamine.)

Based on the known facts, the researchers decided to look for correlations between a measure of divergent thinking and D2BP in the thalamus and the striatum. What they found was that, indeed, there was a significant (p=.013) negative correlation, in a relatively small sample of healthy (non-schizophrenic) individuals, between a measure of divergent thinking and D2BP in the thalamus. There was not a similar correlation in the striatum.

In other words, non-schizophrenic people who had lower dopamine activity in the thalamus tended to have higher divergent thinking scores. This is pretty interesting in itself, especially since other studies have shown lower D2BP in the thalamus to be correlated with higher scores for pathological symptoms in schizophrenics.

What, then, is known about the function of the thalamus? It's a left-right midplane symmetric structure, situated between the cerebral cortex and the midbrain. It has a number of functions, especially as a relay station between the cortex and various subcortical areas. In particular, all sensory signals (except smell) pass through substructures of the thalamus on their way to the part of the cortex that processes them. The thalamus is also thought to be important for regulation of sleep, wakefulness, and consciousness – which makes sense, as it's in a position to control what sensory signals get through.

But why do the dopaminergic neurons of the thalamus have something to do with divergent thinking? The present research doesn't explicitly say anything about that. But the researchers suggest some hypotheses:

Based on the current findings, we suggest that a lower D2BP in the thalamus may be one factor that facilitates performance on divergent thinking tasks. The thalamus contains the highest levels of dopamine D2 receptors out of all extrastriatal brain regions. Decreased D2BP in the thalamus has been suggested, firstly, to lower thalamic gating thresholds, resulting in decreased filtering and autoregulation of information flow, and, secondly, to increase excitation of cortical regions through decreased inhibition of prefrontal pyramidal neurons. The decreased prefrontal signal-to-noise ratio may place networks of cortical neurons in a more labile state, allowing them to more easily switch between representations and process multiple stimuli across a wider association range.

Stated more clearly, perhaps, though less precisely, it seems that lower dopamine activity in the thalamus may allow a freer flow of associations to reach the cortex, which is where higher-level cognition takes place. At the same time, however, if this effect is too strong, the result could be cortical activity that is, pathologically, too chaotic.

de Manzano, �., Cervenka, S., Karabanov, A., Farde, L., & Ullén, F. (2010). Thinking Outside a Less Intact Box: Thalamic Dopamine D2 Receptor Densities Are Negatively Related to Psychometric Creativity in Healthy Individuals PLoS ONE, 5 (5) DOI: 10.1371/journal.pone.0010670

Further reading:

Creativity linked to mental health (5/18/10)

Link Between Creativity and Mental Illness Revealed (5/19/10)

More brains and bonkers connection: thinking out of a broken box (5/24/10)

Dopamine receptor binding potential in the thalamus and creativity (6/1/10)

Creative madness (8/1/10)

Related articles:

Sugar can be addictive (1/11/09)

Dopamine and obesity (11/17/08)

Selected readings 6/13/10

2010-06-13T10:44:00.000-07:00

Anticipating the first steps beyond the Standard Model: Physicists’ knowledge of elementary particles is encapsulated in the Standard Model of particle physics, which currently describes almost everything we’ve seen. Yet there is compelling evidence that the Standard Model cannot be the complete description of nature. For example, despite all of its successes, the Standard Model describes only 20 percent of the mass of the Universe. Eighty percent of the mass is known as “dark matter,” which we have never directly observed and know next to nothing about. [Symmetry Breaking, 6/3/10]
Could DZero result point to multiple Higgses?: What caused the DZero result’s large deviation from Standard Model predictions is just as earth-shaking a mystery. The answer could point to the completion of the Standard Model, missing only the theorized Higgs boson particle, or the creation of a new story line for a host of new particles in the saga of how matter in the universe behaves. In their quest for a full explanation, scientists debate whether they are simply missing a chapter in the Standard Model or if they need a sequel that goes beyond the model, potentially including extra dimensions or a theory called supersymmetry that would double the number of known particles. [Symmetry Breaking, 6/4/10]
What is a "law of physics," anyway?: Why should nature be governed by laws? Why should those laws be expressible in terms of mathematics? Why should they be formulated within space and time? These were the questions posed at a fascinating workshop two weeks ago at the Perimeter Institute, the sequel to a workshop held at Arizona State University in December 2008. ... The bottom line is that the organizers had better start planning on more sequels, because the questions seem as intractable as ever. [Scientific American, 6/4/10]
What a shoddy piece of work is man: The human body is certainly no masterpiece of intelligent planning. The eye's retina, for instance, is wired back to front so that the wiring has to pass back through the screen of light receptors, imposing a blind spot. Now John Avise, an evolutionary geneticist at the University of California at Irvine, has catalogued the array of clumsy flaws and inefficiencies at the fundamental level of the genome. His paper ... throws down the gauntlet to advocates of Intelligent design, the pseudo-scientific face of religious creationism. What Intelligent Designer, Avise asks, would make such a botch? [Nature News, 5/3/10]
Illuminating the brain: Now though, advances in a five-year-old field called optogenetics are convincing these scientists to crack open molecular-biology textbooks. Using a hybrid of genetics, virology and optics, the techniques involved enable researchers to instantaneously activate or silence specific groups of neurons within circuits with a precision that electrophysiology and other standard methods do not allow. Systems neuroscientists have longed for such an advance, which allows them their first real opportunity to pick apart the labyrinthine jumble of cell types in a circuit and test what each one does. [Nature News, 5/5/10]
The code within the code: 95% of the human genome is alternatively spliced, and that changes in this process accompany many diseases. But no one knew how to predict which form of a particular gene would be expressed in a given tissue. "The splicing code is a problem that we've been bashing our heads against for years," says Burge. "Now we finally have the technologies we need." [Nature News, 5/5/10]
European and Asian genomes have traces of Neanderthal: The genomes of most modern humans are 1–4% Neanderthal — a result of interbreeding with the close relatives that went extinct 30,000 years ago, according to work by an international group of researchers. [Nature News, 5/6/10]
Linux vs. Genome in Network Challenge: A comparison of the networks formed by genetic code and the Linux operating system has given insight into the fundamental differences between biological and computational programming. The shapes are very dissimilar, reflecting the evolutionary parameters of each process. Biology is driven by random mutations and natural selection. Software is an act of intelligent design. [Wired, 5/5/10]
Complex Life Traced to Ancient Gene Parasites: Mysterious gene structures called introns that help make complex organisms possible are descended from DNA parasites that infested bacteria billions of years ago, according to a new study. ... The findings fit the notion that group II introns flourished in the early Earth’s heat, and were ultimately co-opted into their hosts’ genomes. [Wired, 6/9/10]
The Magical Mystery Tour: Cassini, the first spacecraft to orbit Saturn, has revealed intricate details of the gas giant planet and its moons -- but many mysteries remain. Six years ago, the Cassini spacecraft began orbiting Saturn and taking detailed images of its ring and many moons. While the Cassini-Huygens mission has helped answer questions about this planetary system, it also has revealed new mysteries for scientists to puzzle over. [Physorg.com, 5/5/10]
Peptides may hold 'missing link' to life: Scientists have discovered that simple peptides can organize into bi-layer membranes. The finding suggests a "missing link" between the pre-biotic Earth's chemical inventory and the organizational scaffolding essential to life. [Physorg.com, 5/6/10]
Physicists study how moral behaviour evolved: A statistical-physics-based model may shed light on the age-old question "how can morality take root in a world where everyone is out for themselves?" Computer simulations by an international team of scientists suggest that the answer lies in how people interact with their closest neighbours rather than with the population as a whole. [Physicsworld.com, 5/5/10]

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Selected readings 6/6/10

2010-06-06T19:14:00.000-07:00

Einstein (Still) Rules The Universe: The pair of independent studies each used observations from NASA's Chandra X-ray Observatory to test Einstein's theory of General Relativity, and to study the properties of gravity on cosmic scales. Both demonstrated that Einstein's theory continues to hold true almost a century after it was first published. [Space.com, 4/23/10]
Listening for the 'birth cries' of black holes: We're talking about the astronomical stuff of nightmares - gargantuan explosions that rip apart giant stars to create black holes. Artist's impression of jets emerging from a dying starThese events are detected in space every few days thanks to Nasa's Swift observatory. The spacecraft sits above the Earth hunting for gamma-ray bursts (GRBs), the intensely bright but fleeting flashes of very high-energy radiation that can sweep our way from all points in the sky.
[BBC News, 4/20/10]
Hubble's role in search for aliens: The powerful vision of the Hubble Telescope - which turns 20 this week - has expanded our cosmic horizons and brought into sharper focus a new set of mysteries about the universe that is our home. To those whose science is gleaned from the media, astronomy may seem to be on a roll. And it is. [BBC News, 4/22/10]
Revealing the True Solar Corona: A total solar eclipse—the Moon blocking out the entire body of the Sun—actually reveals great detail of the Sun’s structure. When the blinding brilliance of the Sun is obscured, this allows its more tenuous surrounding features—its corona—to come into view. Investigating the corona may seem straightforward, but it requires an understanding beyond seeing, imaging and modeling. [American Scientist, 5/1/10]
Convincing the Public to Accept New Medical Guidelines: A $1.1 billion provision in the federal stimulus package aims to address the issue by providing funds for comparative effectiveness research to find the most effective treatments for common conditions. But these efforts are bound to face resistance when they challenge existing beliefs. As Nieman and countless other researchers have learned, new evidence often meets with dismay or even outrage when it shifts recommendations away from popular practices or debunks widely held beliefs. [Miller-McCune Online, 4/20/10]
Terra Incognita: The essential question is not whether you do or don't believe in a fundamental theory of everything. The essential question is what is a good and promising way to expand what is known. You can believe in flying spaghetti monsters, reincarnation, or a theory of everything: if it helps you with your research, by all means, go ahead, just don't put your believes in the abstract of your paper. [Backreaction, 5/21/10]
Protons not as “strange” as expected: The G-Zero collaboration proposed a precisely tuned survey for ephemeral particles that appear only briefly inside matter. Specifically, they wanted to measure the effect of strange particles in the proton, the sub-atomic particle found deep inside the nucleus of every atom in our universe. [Symmetry Breaking, 4/27/10]
Signs of dark matter may point to mirror matter candidate: Mirror matter would interact very weakly with ordinary matter. For this reason, some physicists have speculated that mirror particles could be candidates for dark matter. Even though mirror matter would produce light, we would not see it, and it would be very difficult to detect. [Physorg.com, 4/27/10]
Earth's Climate Used to Weigh Chances of Alien Life: Greenhouse gases have a bad reputation because of the role they're playing in global warming on Earth today. However, scientists say we also owe our lives to greenhouse gases because they might have allowed life to take hold in the first place. A new study of how these and other climate conditions have affected the origin and evolution of life on Earth could provide clues to understanding how climates on alien planets might affect their potential life. [Space.com, 6/3/10]
Evidence grows for tetraquarks: The existence of a new form of matter called a tetraquark has been given further support by the re-analysis of an experiment that has baffled particle physicists for the past two years. [Physicsworld.com, 4/27/10]
The cancer genome challenge: In the past two years, labs around the world have teamed up to sequence the DNA from thousands of tumours along with healthy cells from the same individuals. Roughly 75 cancer genomes have been sequenced to some extent and published; researchers expect to have several hundred completed sequences by the end of the year. [Nature News, 4/14/10]
Biomarker Studies Could Realize Goal of More Effective and Personalized Cancer Medicine: Biological and genomic studies are showing that most types of cancer are not single diseases, but rather complex disorders with distinct causes. Take breast cancer, for example: "When we say 'breast cancer', we're probably lumping 15 different diseases into that category," says co-author Joseph Nevins.... Subtle differences in the tumors' genomes and genetic expression are what make drugs work in certain patients and not in others. [Scientific American, 4/26/10]

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Selected readings 5/31/10

2010-05-31T11:50:00.001-07:00

Seeing Aliens Will Likely Take Centuries: Although our telescopes will likely become good enough to detect signs of life on exoplanets within the next 100 years, it would probably take many centuries before we could ever get a good look at the aliens. "Unfortunately, we are perhaps as far away from seeing aliens with our own eyes as Epicurus was from seeing the first other worlds when, 23 centuries ago, he predicted the existence of these planets," said astrobiologist Jean Schneider at the Paris Observatory at Meudon. [Space.com, 4/29/10]
Only a matter of time, says Frank Drake: The search for extraterrestrial intelligence began in earnest 50 years ago, led by a young American astronomer named Frank Drake - a man, who is still confident we'll eventually find extraterrestrial civilisations. [COSMOS Magazine, 4/7/10]
A review of the Drake Equation: Which is the more shocking proposition: that our galactic neighbourhood is riddled with advanced alien civilisations? Or that we humans are a solitary beacon of intelligent life in a silent universe of almost incomprehensible vastness? Either prospect is enough to keep you awake at night. Yet one of these two statements is likely true. We just don't know which one. [COSMOS Magazine, 4/7/10]
What's up with nanotech?: While nanotechnology — working at a scale that is one-thousandth the width of a human hair — may have faded from the public’s imagination, the field has made substantial progress in recent years, opening new frontiers in electronics, medicine, and materials. [Boston.com, 3/29/10]
Scientist who cloned Dolly the sheep sees revolution in disease treatment in 20 years: The scientist who cloned Dolly the sheep believes that a new approach to the production of stem cells could revolutionise the treatment of inherited diseases such as Parkinson’s and motor neurone disease “within ten to twenty years”. [Times Online, 3/26/10]
Next Big Thing in English: Knowing They Know That You Know: This layered process of figuring out what someone else is thinking — of mind reading — is both a common literary device and an essential survival skill. Why human beings are equipped with this capacity and what particular brain functions enable them to do it are questions that have occupied primarily cognitive psychologists. [New York Times, 3/31/10]
Telescope arrays give fine view of stars: Radio astronomers have relied on interferometry for more than half a century, but optical astronomers have lagged behind. Now, optical interferometry has come of age. [Nature News, 4/7/10]
Protein folding: The dark side of proteins: Almost every human protein has segments that can form amyloids, the sticky aggregates known for their role in disease. Yet cells have evolved some elaborate defences. [Nature News, 4/7/10]
A New Clue to Explain Existence: Physicists at the Fermi National Accelerator Laboratory are reporting that they have discovered a new clue that could help unravel one of the biggest mysteries of cosmology: why the universe is composed of matter and not its evil-twin opposite, antimatter. [New York Times, 5/17/10]
Fermilab scientists find evidence for significant matter-antimatter asymmetry: The dominance of matter that we observe in the universe is possible only if there are differences in the behavior of particles and antiparticles. Although physicists have observed such differences (called “CP violation”) in particle behavior for decades, these known differences are much too small to explain the observed dominance of matter over antimatter in the universe and are fully consistent with the Standard Model. If confirmed by further observations and analysis, the effect seen by DZero physicists could represent another step towards understanding the observed matter dominance by pointing to new physics phenomena beyond what we know today. [SymmetryBreaking, 5/18/10]
How Many Sparks in the Genome?: The first two categories include stretches of DNA that are useful. The second two include stretches that are useless. Now comes the hard part: figuring out just how much of the genome is made up of each. [The Loom, 5/19/10]
Supermassive Black Holes Can Kill Whole Galaxies: Astrophysicists have found that when a supermassive black hole quickly devours gas and dust, it can generate enough radiation to abort all the embryonic stars in the surrounding galaxy. [ScienceNOW, 4/15/10]
The Search for Genes Leads to Unexpected Places: Dr. Marcotte and his colleagues have discovered hundreds of other genes involved in human disorders by looking at distantly related species. They have found genes associated with deafness in plants, for example, and genes associated with breast cancer in nematode worms. [New York Times, 4/26/10]
Life on Titan: stand well back and hold your nose!: Research by astrobiologist William Bains suggests that if life has evolved on the frozen surface of Saturn's moon, Titan, it would be strange, smelly and explosive compared to life on Earth. [Physorg.com, 4/14/10]
Perhaps a longer lifespan, certainly a longer 'health span': Organisms from yeast to rodents to humans all benefit from cutting calories. In less complex organisms, restricting calories can double or even triple lifespan. It's not yet clear just how much longer calorie restriction might help humans live, but those who practice the strict diet hope to survive past 100 years old. [Physorg.com, 4/15/10]
Hubble Space Telescope clocks up 20 years: It was an instrument that much of the astronomical community didn't want, but times change: to get time now on the Hubble Space Telescope, which is celebrating its 20th anniversary this week, an astronomer usually faces competition from at least 11 other eager scientists. [Nature News, 4/22/10]
Origin of Life Chicken-and-Egg Problem Solved: Scientists have wondered how the first simple, self-replicating chemicals could have formed complex, information-rich genetic structures, when replication was originally such an error-prone process. Every advance would soon be lost to copying errors. According to a new study, the answer may lie in the fundamental nature of those chemicals. The errors may have triggered an automatic shutdown of replication. Such stalling would allow only error-free sequences to be completed, giving them a chance at evolving. [Wired, 4/22/10]
A Skeptic Questions Cancer Genome Projects: Fueled by hundreds of millions of grant dollars, biomedical researchers have begun sequencing the genomes of thousands of tumor samples in the past few years, linking up scores of labs and sequencing centers in a massive effort to identify the genes behind major cancers. But a leading cancer geneticist this week questioned whether this strategy still makes sense. [ScienceInsider, 4/23/10]
Black holes and qubits: While string theory and M-theory have yet to make readily testable predictions in high-energy physics, they could find practical applications in quantum-information theory. [CERN Courier, 5/5/10]
Neutrinos: Clues to the Most Energetic Cosmic Rays: ARIANNA, a proposed array of detectors for capturing the most energetic cosmic rays, is being tested in Antarctica with a prototype station built last December on the Ross Ice Shelf by a Berkeley Lab team. By detecting neutrino-generated signals bounced off the interface of water and ice beneath the shelf, scientists hope to pinpoint the still unidentified sources of ultra-high-energy cosmic rays. [Physorg.com, 4/20/10]
In praise of the Y chromosome: David Page, director of the Whitehead Institute and professor of biology at Massachusetts Institute of Technology, says research indicates the much-maligned Y chromosome plays a more critical role in genetics than previously believed. [Physorg.com, 4/20/10]
The Evolution of the End: Immortality comes with some fairly significant disadvantages. A large complex organism requires a good bit of resources and the environment offers only so many available niches in which organisms of a set design can live. If the landscape is already saturated by unaging oldsters doing their timeless thing, there's little room for new and at least possibly improved models to take the stage. For most organisms, the areas where life is most tenuous is at the ends; both predators and disease take the hardest toll on the very young and the very old. If there are no old, then additional stress could be placed on the newcomers, further cutting turnover in a population. That means little chance for newbies, with their occasional mutations and interesting new combinations of genes. For immortals, evolution runs in slow motion. [Daily Kos, 5/30/10]
The Rise of the Mind: When and where did the cognitive abilities of modern humans arise? It's a big question -- one debated by anthropologists for decades. It's an even bigger question for an undergraduate thesis, but senior Logan Bartram has a leg up on this ambitious project: he helped unearth artifacts that are playing a critical role in shaping our knowledge about human origins. [Physorg.com, 4/22/10]
Airport security: Intent to deceive?: To Honts, the decade since the 11 September attacks has been one of lost opportunity. Calling SPOT an "abject failure", he says that the government would have done better to invest first in basic science, experimentally establishing how people with malintent think and respond during screenings. That work, in turn, could have laid a more solid foundation for effective detection methods. [Nature News, 5/26/10]

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The Glow of the Lagoon Nebula

2010-05-29T19:16:00.000-07:00

The Glow of the Lagoon Nebula

Gas and dust condense, beginning the process of creating new stars in this image of Messier 8, also known as the Lagoon Nebula. Located four to five thousand light-years away, in the constellation of Sagittarius (the Archer), the nebula is a giant interstellar cloud, one hundred light-years across. It boasts many large, hot stars, whose ultraviolet radiation sculpts the gas and dust into unusual shapes. Two of these giant stars illuminate the brightest part of the nebula, known as the Hourglass Nebula, a spiralling, funnel-like shape near its centre. Messier 8 is one of the few star-forming nebulae visible to the unaided eye, and was discovered as long ago as 1747, although the full range of colours wasn’t visible until the advent of more powerful telescopes. The Lagoon Nebula derives its name from the wide lagoon-shaped dark lane located in the middle of the nebula that divides it into two glowing sections.

Lagoon Nebula – click for 1280×1303 image

Soul Nebula

2010-05-12T23:52:00.000-07:00

Soul Nebula (4/2/10)

This WISE mosaic is of the Soul Nebula (a.k.a. the Embryo Nebula, IC 1848, or W5). It is an open cluster of stars surrounded by a cloud of dust and gas over 150 light-years across and located about 6,500 light-years from Earth in the constellation Cassiopeia, near the Heart Nebula (partially seen in the WISE image of Maffei 1 & 2).

The cluster of stars, IC 1848, formed about a million years ago from the material of the nebula. Winds and ultraviolet light from these young stars are excavating a cavity in the cloud. Parts of the cloud that are more dense than their surroundings are being eroded more slowly and form giant towers, or pillars of dust and gas, which all point toward the central star cluster. It’s reminiscent of the landscape of Badlands National Park in South Dakota. Material at the interior edges of the cavity is also being compressed by the winds and radiation from the star cluster. This triggers new star formation in those areas. The pillars inside the Soul Nebula are each about 10 light-years tall and have stars forming at their tips.

Soul Nebula – click for 800×418 image

Where the action is in black hole jets

2010-05-12T20:23:00.000-07:00

The object known simply as 3C 279 is rather distinctive for several reasons, in spite of the rather unassuming name. For one thing it's an active galaxy – that is, it has a supermassive black hole at its center, and that black hole is sucking in surrounding matter at a rate high enough to generate as much energy as all stars the in the galaxy where it resides combined. Only about 1% of visible galaxies are active galaxies like 3C 279.

But that's not all. 3C 279 is also a radio galaxy, a subset of only about 10% of active galaxies that also feature strong radio-frequency emissions. Such strong emissions are generally thought to be produced by a violent outflow of matter from the vicinity of the black hole in the form of narrow jets. The flow is so violent that matter in the jets reaches velocities close to the velocity of light.

And if that's not enough, one of the jets of 3C 279 is pointed almost straight at us. Only a few percent of active radio galaxies are oriented that way, by chance. Because we're looking essentially straight into the most active part of the object, with basically no dust or gas to obscure the view, 3C 279 appears especially luminous – the term for such an object is "blazar".

Although its jet is aimed right at us, there's nothing to be particularly concerned about, since 3C 279 has a redshift of z=0.536, which means it's actually about 6.5 billion light years away.

3C 279

I just wrote at some length about active galaxies, here, in some detail, so you might like to review that if you need to refresh your memory on many basics of the subject. There may be some aspects of the present discussion that will make more sense in light of that.

Even though 3C 279 came to the attention of astronomers over 40 years ago, because of its unusual apparent brightness and radio emissions, it is not an especially powerful active galaxy, as those things go. The central black hole is estimated to have a mass around 6×10⁸ M_⊙, somewhat short of 10⁹ M_⊙ that is typical of the largest quasars.

The peak velocity of matter in the jet of 3C 279 has been inferred to be about 99.8% of the speed of light, which is "relativistic" by anyone's definition. In other words, this velocity is v=0.998c. It's customary to express this velocity as β = v/c = 0.998. The inference is based on apparent (but not real) "superluminal" (faster than light) motion of jet-related material. This is a common phenomenon seen in active galaxy jets that are nearly parallel to our line of sight. A related quantity, the Lorentz factor, is defined as γ = (1-β²)^-1/2, so in this case γ ≈ 16. That'll play a role in an important calculation later.

Since astronomers have been interested in 3C 279 for over 40 years, it's been studied a lot, although that's been difficult, because of its rather large distance. Radio galaxies like this produce electromagnetic emissions all the way from radio frequencies on up to gamma rays – spanning 11 or 12 orders of magnitude in photon energy, from under .001 eV to over 100 Mev. Many of those frequency ranges can be observed only from instruments in space, so until recently it hasn't been possible to observe a single object continuously for long periods of time in many bands. This has now been done for the blazar 3C 279 – and perhaps by chance something rather interesting showed up, which could only have been observed in an active galaxy whose jet is nearly parallel to our line of sight.

A change in the optical polarization associated with a γ-ray flare in the blazar 3C 279

It is widely accepted that strong and variable radiation detected over all accessible energy bands in a number of active galaxies arises from a relativistic, Doppler-boosted jet pointing close to our line of sight. The size of the emitting zone and the location of this region relative to the central supermassive black hole are, however, poorly known, with estimates ranging from light-hours to a light-year or more. Here we report the coincidence of a gamma (γ)-ray flare with a dramatic change of optical polarization angle. This provides evidence for co-spatiality of optical and γ-ray emission regions and indicates a highly ordered jet magnetic field. The results also require a non-axisymmetric structure of the emission zone, implying a curved trajectory for the emitting material within the jet, with the dissipation region located at a considerable distance from the black hole, at about 10⁵ gravitational radii.

The main thing that this paper reports is an "event", evidently some sort of disturbance affecting the jet, manifested in the spectrum of 3C 329. The event was most pronounced in the γ-ray part of the spectrum, which – in this object – is the dominant and also the most variable part. The γ-ray flux of 3C 279 can vary over an order of magnitude, and at one point – the beginning of the event – the flux increased rapidly from an already elevated level to its maximum value, then dropped a little more slowly, over a span of 20 days, to its minimum.

Other parts of the spectrum were also affected, but not so dramatically. Flux in ultraviolet, optical, and near infrared bands also decreased from somewhat elevated levels during the same 20 days, though there was no spike up at the start. There was, however, little change in the X-ray and radio bands during this period.

There was one additional dramatic change in the same period. The percentage of polarization in optical emissions (blue) dropped from 30-40% down to 10% before recovering at the end of the period. And at the same time, the direction of polarization changed smoothly over the 20 days by about 180°.

Since our line of sight is nearly parallel (to within about 2°) to the jet, it is difficult to distinguish where in 3C 279 different emissions originate. Strong γ-ray emissions are typically associated with jets (when present), but a key question that the paper examines concerns what part of the jet the dramatic changes in γ-ray flux could have been associated with. Was it relatively close to the black hole, or much farther out?

It's not too surprising that there was little change in X-ray flux, since that's normally associated in active galaxies with the "corona", which is symmetrically distributed in a region with a radius of a few hundred light years around the black hole. Radio emissions, however, do generally originate from the jets, but often from "lobes" at very large distances from the center. In this case it would seem that the source of radio emissions had little to do with the "event".

On the other hand, since distinct changes in ultraviolet, optical, and infrared flux – as well as the dramatic change in polarization – occurred at exactly the same time as the γ-ray "event", it's natural to suppose that whatever caused the disturbance affected a part of the jet where these emissions originated.

So what can be said about the size and (perhaps) location of the disturbance? The key fact is that the event was observed to last 20 days. However, since we're dealing with matter moving at a relativistic velocity, it doesn't at all follow that the disturbance affected only a portion of the jet about 20 light days in extent. It's not hard to calculate the "actual" size of the disturbance, but it does take a little work.

Suppose we let r₀ be the distance along the jet from the central black hole at which the disturbance began, and r₁ be the distance at which the state of the jet has returned to "normal". Then r₁ >r₀. The distance d = r₁ - r₀ is what we want to compute. If v is the average velocity of matter in the jet when the event occurred, then we have already noted v = 0.998c, so that β =v/c = 0.998.

Note that d is the distance in our reference frame. The time (in our frame) it takes light to travel that distance is d/c. If we assume that the matter within the jet that's subject to the disturbance is moving with velocity v, then the time it takes the leading edge of that matter to go the same distance is d/v. Since c > v, d/v > d/c, so by the time the leading edge reaches r₁ it is lagging behind the corresponding photons by a time interval Δt = d/v-d/c > 0. Since we're aiming only for an approximation, assume for simplicity that the spatial extent of the disturbance (from leading to trailing edge) is small compared to d. Then the photons from the time the disturbance began at r₀ will reach us by the same interval Δt ahead of the photons from the time the disturbance ended, when the affected matter was at r₁.

So the data we have to work with are just β and the observed elapsed time between the start and end of the event: Δt ≈ 20 days. We'll get an expression for d in terms of Δt.

We have Δt = d/v-d/c = (d/c)(c-v)/v = (d/c)(1-β)/β. Multiplying that by (1+β)/(1+β) gives Δt = (d/c)(1-β²)/[β(1+β)]. Using 1-β² = 1/γ² and solving for d gives d = γ²cΔtβ(1+β). But in this example, β≈1, so d ≈ 2γ²cΔt.

Plugging in actual numbers, Δt≈1.7×10⁶ seconds, c≈3×10⁸ m/sec, and γ²≈256 gives d≈2.6×10¹⁷ m. A light year is about 9.5×10¹⁵ m, so d is about 27 light years. That's quite an extensive part of 3C 279's jet that is affected by the disturbance.

Another way to appreciate the size of that number is to compare it to the Schwarzschild radius of the black hole, r_s=2GM_BH/c². M_BH is roughly 6×10⁸ M_⊙, so with G=6.67×10^-11 m³ kg^-1 sec^-2 and M_⊙=1.99×10³⁰ kg, we find r_s≈1.8×10¹² m. Thus the size of the disturbance is more than 100 thousand times the black hole's Schwarzschild radius – 5 orders of magnitude.

So, now that we have some idea of the impressive extent of this "disturbance", is it possible to draw any conclusions about what caused it?

To begin with, keep in mind that we have assumed the matter that is disturbed is propagating along the jet with velocity v=0.998c. That assumption is the reason the estimate of d is so large, because of the factor γ². If v≪c, then β≈0 and γ≈1, so that d ≈ cΔt ≈ 5×10¹⁴ m – about a factor of 500 smaller. In this latter case the disturbance affects the jet only in a small zone at a distance of r₀ from the black hole, and the matter "flows through" this zone without much long-lasting effect. This could happen, for example, if there is a narrow knot in the magnetic fields that keep the jet constricted.

The evidence that this latter possibility is not in fact what's happening is that the polarization of light turns around by 180° in almost perfect synchrony with the event in which γ-ray flux has a large bump. This implies that there's a large-scale bend in the jet at that point, so that the direction of the jet crosses over our line of sight. This apparent change of direction persists far longer than the event itself.

Of course, that hypothesis still doesn't explain either the γ-ray flare or the change of direction itself. It is possible, for instance, that the jet encounters, at an oblique angle, some large concentration of matter that deflects the jet. Perhaps the jet passes very close to another black hole. We simply don't know.

There was no guarantee that we could quickly learn how to explain all the behavior of black hole jets with ease – so the observational effort must continue, with increasingly sensitive equipment and larger data sets.

Abdo, A., Ackermann, M., Ajello, M., Axelsson, M., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Baughman, B., Bechtol, K., Bellazzini, R., Berenji, B., Blandford, R., Bloom, E., Bock, D., Bogart, J., Bonamente, E., Borgland, A., Bouvier, A., Bregeon, J., Brez, A., Brigida, M., Bruel, P., Burnett, T., Buson, S., Caliandro, G., Cameron, R., Caraveo, P., Casandjian, J., Cavazzuti, E., Cecchi, C., Çelik, �., Chekhtman, A., Cheung, C., Chiang, J., Ciprini, S., Claus, R., Cohen-Tanugi, J., Collmar, W., Cominsky, L., Conrad, J., Corbel, S., Corbet, R., Costamante, L., Cutini, S., Dermer, C., de Angelis, A., de Palma, F., Digel, S., do Couto e Silva, E., Drell, P., Dubois, R., Dumora, D., Farnier, C., Favuzzi, C., Fegan, S., Ferrara, E., Focke, W., Fortin, P., Frailis, M., Fuhrmann, L., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Gehrels, N., Germani, S., Giebels, B., Giglietto, N., Giommi, P., Giordano, F., Giroletti, M., Glanzman, T., Godfrey, G., Grenier, I., Grove, J., Guillemot, L., Guiriec, S., Hanabata, Y., Harding, A., Hayashida, M., Hays, E., Horan, D., Hughes, R., Iafrate, G., Itoh, R., Jackson, M., Jóhannesson, G., Johnson, A., Johnson, W., Kadler, M., Kamae, T., Katagiri, H., Kataoka, J., Kawai, N., Kerr, M., Knödlseder, J., Kocian, M., Kuss, M., Lande, J., Larsson, S., Latronico, L., Lemoine-Goumard, M., Longo, F., Loparco, F., Lott, B., Lovellette, M., Lubrano, P., Macquart, J., Madejski, G., Makeev, A., Max-Moerbeck, W., Mazziotta, M., McConville, W., McEnery, J., McGlynn, S., Meurer, C., Michelson, P., Mitthumsiri, W., Mizuno, T., Moiseev, A., Monte, C., Monzani, M., Morselli, A., Moskalenko, I., Murgia, S., Nestoras, I., Nolan, P., Norris, J., Nuss, E., Ohsugi, T., Okumura, A., Omodei, N., Orlando, E., Ormes, J., Paneque, D., Panetta, J., Parent, D., Pavlidou, V., Pearson, T., Pelassa, V., Pepe, M., Pesce-Rollins, M., Piron, F., Porter, T., Rainò, S., Rando, R., Razzano, M., Readhead, A., Reimer, A., Reimer, O., Reposeur, T., Reyes, L., Richards, J., Rochester, L., Rodriguez, A., Roth, M., Ryde, F., Sadrozinski, H., Sanchez, D., Sander, A., Saz Parkinson, P., Scargle, J., Sgrò, C., Shaw, M., Shrader, C., Siskind, E., Smith, D., Smith, P., Spandre, G., Spinelli, P., Stawarz, L., Stevenson, M., Strickman, M., Suson, D., Tajima, H., Takahashi, H., Takahashi, T., Tanaka, T., Taylor, G., Thayer, J., Thayer, J., Thompson, D., Tibaldo, L., Torres, D., Tosti, G., Tramacere, A., Uchiyama, Y., Usher, T., Vasileiou, V., Vilchez, N., Vitale, V., Waite, A., Wang, P., Wehrle, A., Winer, B., Wood, K., Ylinen, T., Zensus, J., Ziegler, M., Uemura, M., Ikejiri, Y., Kawabata, K., Kino, M., Sakimoto, K., Sasada, M., Sato, S., Yamanaka, M., Villata, M., Raiteri, C., Agudo, I., Aller, H., Aller, M., Angelakis, E., Arkharov, A., Bach, U., Benítez, E., Berdyugin, A., Blinov, D., Boettcher, M., Buemi, C., Chen, W., Dolci, M., Dultzin, D., Efimova, N., Gurwell, M., Gusbar, C., Gómez, J., Heidt, J., Hiriart, D., Hovatta, T., Jorstad, S., Konstantinova, T., Kopatskaya, E., Koptelova, E., Kurtanidze, O., Lahteenmaki, A., Larionov, V., Larionova, E., Leto, P., Lin, H., Lindfors, E., Marscher, A., McHardy, I., Melnichuk, D., Mommert, M., Nilsson, K., Di Paola, A., Reinthal, R., Richter, G., Roca-Sogorb, M., Roustazadeh, P., Sigua, L., Takalo, L., Tornikoski, M., Trigilio, C., Troitsky, I., Umana, G., Villforth, C., Grainge, K., Moderski, R., Nalewajko, K., & Sikora, M. (2010). A change in the optical polarization associated with a γ-ray flare in the blazar 3C 279 Nature, 463 (7283), 919-923 DOI: 10.1038/nature08841

Further reading:

Extreme Jets Take New Shape (2/17/10)

Fermi pins down a colossal accelerator (2/18/10)

Astrophysics: Cosmic jet engines (2/18/10)

Related articles:

Active galaxies and supermassive black hole jets (4/25/10)

Winds of Change: How Black Holes May Shape Galaxies (4/19/10)

Galactic black holes may be more massive than thought (6/8/09)

Black hole outflows from Centaurus A (2/6/09)

Evidence that quasars are powered by black holes (10/21/06)

The wind from a black hole (7/8/06)

Selected readings 5/8/10

2010-05-08T23:59:00.000-07:00

Interesting reading and news items.

These items are also bookmarked at my Diigo account.

The Search for Genes Leads to Unexpected Places: Dr. Marcotte and his colleagues have discovered hundreds of other genes involved in human disorders by looking at distantly related species. They have found genes associated with deafness in plants, for example, and genes associated with breast cancer in nematode worms. [New York Times, 4/26/10]
Are we there yet?: Years of effort and roughly 10,000 people have made the Large Hadron Collider the most powerful particle accelerator in the world. This collaborative feat of technology promises to change the way we understand the universe. Now the world is watching, waiting to see what so much effort will yield. Even at an initial collision energy of 7 trillion electronvolts-half its full capacity-the LHC is in a position to make important discoveries. [Symmetry, 4/1/10]
Moving beyond silicon to break the MegaHertz barrier: We're rapidly closing in on a decade since the first desktop processors cleared the 3GHz mark, but in a stunning break from earlier progress, the clock speed of the top processors has stayed roughly in the same neighborhood since. Meanwhile, the feature shrinks that have at least added additional processing cores to the hardware are edging up to the limits of photolithography technology. [Nobel Intent, 3/26/10]
How huge particle detectors actually detect tiny particles: The detectors in colliders like the Large Hadron Collider and Relativistic Heavy Ion Collider work by looking at some of the items that come rocketing out of the collisions, producing the sort of traces shown here. Given that data, it's possible for physicists to work their way backwards in order to figure out what went on in the collision itself. [Nobel Intent, 3/29/10]
The software brains behind the particle colliders: In the instant that its detectors register the events associated with a collision, the challenges move from the hardware realm into software, as the LHC will literally produce more data than we can possibly handle. We have to figure out what to hang on to in real time, and send it around the globe via dedicated connections that aggregate multiple 10Gbp/s links; those on the receiving end need to safely store it and pursue the sorts of analyses that will hopefully reveal some new physics. [Nobel Intent, 3/30/10]
Lasing Beyond Light: Now, at age 50, the laser has extended its dominion far beyond the realm of light. Physicists have succeeded in building lasers that emit different kinds of waves. Laserlike “hard” X-ray pulses, for example, can freeze atoms in their tracks, providing a ringside view of chemical reactions. And phonon lasers vault the technology out of the electromagnetic spectrum altogether, creating coherent beams of sound. [Science News, 4/23/10]
Master of the Cell: RNA interference, with its powerful promise of therapy for many diseases, may also act as a master regulator of most-if not all-cellular processes. [The Scientist, 3/29/10]
Obesity: the role of the immune system: Obesity is one symptom of several, which together constitute what is now termed metabolic syndrome. Morbid obesity is also associated with a host of other symptoms including high blood sugar, high blood lipids, insulin resistance and liver disorders. The root causes of which are traced back to excessive food consumption, reduced physical activity and in some cases, genetic predisposition. [Byte Size Biology, 4/25/10]
Evolving a code: A molecular fossil's tale: Every living cell on earth carries a molecular fossil: the ribosome. In a recent paper published in PNAS, researchers from California open the drawer and dust off this ancient molecular machine. The structure of the ribosome seems to provide hints about the origin of that universal feature of life: the genetic code. [Thoughtomics, 4/18/10]
Can Life on Titan Thrive Without Water?: The standard definition of a "habitable world" is a world with liquid water at its surface; the "habitable zone" around a star is defined as that Goldilocks region — not too hot, not too cold — where a watery planet or moon can exist. And then there's Titan. Saturn's giant moon Titan lies about as far from the standard definition of habitable as one can get. The temperature at its surface hovers around 94 degrees Kelvin (minus 179 C, or minus 290 F). At that temperature, water is a rock as hard as granite. And yet many scientists now believe life may have found a way to take hold on Titan. [Space.com, 3/23/10]
Neutrinos: Clues to the Most Energetic Cosmic Rays: “The most energetic cosmic rays are the rarest, and they pose the biggest mystery,” says Spencer Klein of Berkeley Lab’s Nuclear Science Division. He compares the energy of an ultra-high-energy (UHE) cosmic ray to a well-hit tennis ball or a boxer’s punch – all packed into a single atomic nucleus. ... Sources capable of producing such high-energy nuclei have not been clearly identified. One clue to the origin of the highest-energy cosmic rays is the neutrinos they produce when they interact with the very cosmic microwave photons that slow them down. [Berkeley Lab News Center, 4/19/10]
Bizarre models for human diseases: The search for models of human diseases might just have become easier, thanks to a data-mining technique that screens genetic databases to find subtle links to organisms as distant from humans as plants. The new tool integrates information from existing databases that associate gene mutations with observable traits in a range of species, including humans, mice, yeast, worms and plants. And the method identifies genes in the non-human species that are more likely than by chance to contribute to human disease. [Nature News, 3/22/10]
Addicted to Fat: Overeating May Alter the Brain as Much as Hard Drugs: Like many people, rats are happy to gorge themselves on tasty, high-fat treats. Bacon, sausage, chocolate and even cheesecake quickly became favorites of laboratory rats that recently were given access to these human indulgences-so much so that the animals came to depend on high quantities to feel good, like drug users who need to up their intake to get high. A new study, published online March 28 in Nature Neuroscience, describes these rats' indulgent tribulations, adding to research literature on the how excess food intake can trigger changes in the brain, alterations that seem to create a neurochemical dependency in the eater-or user. [Scientific American, 3/28/10]
Fatty foods can be addictive like crack—at least for rats: Obesity may be a result of a reduced sensitivity to the "rewards" of calorically dense food, fostered by eating too much of the stuff too often, according study published in Nature Neuroscience this week. A group of researchers gave some rats different levels of access to tasty and highly caloric "cafeteria" foods, while training them to respond to aversive stimuli. Rats who had been given the most access to the good stuff ignored any indications of negative consequences and kept right on eating. [Nobel Intent, 3/30/10]
Fast machines, genes and the future of medicine: Some experts say the world is on the cusp of a "golden age" of genomics, when a look at the DNA code will reveal your risk of cancer, diabetes or heart disease, and predict which drugs will work for you. Yet the $3 billion international Human Genome Project, whose first phase was completed a decade ago, has not led to a single blockbuster diagnosis or product. [Reuters, 3/30/10]
Bursting the genomics bubble: For scientists, the Human Genome Project (HGP) might lay the foundation of tomorrow's medicine, with drugs tailored to your genetics. But a venture capitalist would want medical innovations here and now, not decades hence. Nearly ten years after the project's formal completion, there's not much sign of them. [Nature News, 3/31/10]
Human genome at ten: Life is complicated: As sequencing and other new technologies spew forth data, the complexity of biology has seemed to grow by orders of magnitude. Delving into it has been like zooming into a Mandelbrot set — a space that is determined by a simple equation, but that reveals ever more intricate patterns as one peers closer at its boundary. [Nature News, 3/31/10]
The trouble with genes: Scientists were shocked when they found out how few 'old-fashioned' genes we actually have - about the same number as the humble nematode worm (Caenorhabditis elegans). In fact, almost all multicellular creatures with the complexity of a worm or greater have about 20,000 genes. But for Mattick, the death knell of the traditional concept of the gene was triggered by another revolution altogether - that of the digital information age. [Cosmos, 4/12/10]
Genome of a killer: What we call cancer is actually a class of 200 diseases in different tissues, which are all caused by cells that have started to multiply out of control. Most treatments are drastic and invasive, such as chemotherapy and surgery. "Cancer is extremely complex, but we are beginning to understand how this complexity works, in terms of which genes are important," says oncologist Victor Velculescu. [Cosmos, 4/27/10]
10 Years on, ‘The Genome Revolution Is Only Just Beginning’: Almost 10 years after the celebrated completion of the human genome’s first draft, the expected revolution in medicine and research has only partly come to pass. The human genome’s sequencing has profoundly influenced basic research and the refinement of genome-reading tools. But those advances have had only limited medical impacts. [Wired, 3/31/10]
Einstein’s theory fights off challengers: Two new and independent studies have put Einstein’s General Theory of Relativity to the test like never before. These results, made using NASA’s Chandra X-ray Observatory, show Einstein’s theory is still the best game in town. Each team of scientists took advantage of extensive Chandra observations of galaxy clusters, the largest objects in the universe bound together by gravity. One result undercuts a rival gravity model to General Relativity, while the other shows that Einstein’s theory works over a vast range of times and distances across the cosmos. [Symmetry Breaking, 4/15/10]
What are 'mini' black holes?: ‘The simplest black holes are objects with a singularity in the centre and that are surrounded by an ‘event horizon’,’ explains Cigdem Issever of Oxford University’s Department of Physics. ‘Once something comes closer to the black hole than the radius of the event horizon, it is not able to leave: even light can’t escape and so the name ‘black hole’ was given to these objects by John Archibald Wheeler back in 1967.’ [Physorg.com, 3/29/10]
A Grand Unified Theory of Artificial Intelligence: In the 1950s and '60s, artificial-intelligence researchers saw themselves as trying to uncover the rules of thought. But those rules turned out to be way more complicated than anyone had imagined. Since then, artificial-intelligence (AI) research has come to rely, instead, on probabilities -- statistical patterns that computers can learn from large sets of training data. [Physorg.com, 3/30/10]
Charting Creativity: Signposts of a Hazy Territory: They hope to figure out precisely which biochemicals, electrical impulses and regions were used when, say, Picasso painted "Guernica," or Louise Nevelson assembled her wooden sculptures. Using M.R.I. technology, researchers are monitoring what goes on inside a person's brain while he or she engages in a creative task. Yet the images of signals flashing across frontal lobes have pushed scientists to re-examine the very way creativity is measured in a laboratory. [New York Times, 5/7/10]

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VISTA’s infrared view of the Cat’s Paw Nebula

2010-05-03T20:23:00.000-07:00

VISTA’s infrared view of the Cat’s Paw Nebula

The Cat’s Paw Nebula, NGC 6334, is a huge stellar nursery, the birthplace of hundreds of massive stars. In a magnificent new ESO image taken with the Visible and Infrared Survey Telescope for Astronomy (VISTA) at the Paranal Observatory in Chile, the glowing gas and dust clouds obscuring the view are penetrated by infrared light and some of the Cat’s hidden young stars are revealed.

Towards the heart of the Milky Way, 5500 light-years from Earth in the constellation of Scorpius (the Scorpion), the Cat’s Paw Nebula stretches across 50 light-years. In visible light, gas and dust are illuminated by hot young stars, creating strange reddish shapes that give the object its nickname. A recent image by ESO’s Wide Field Imager (WFI) at the La Silla Observatory (eso1003) captured this visible light view in great detail. NGC 6334 is one of the most active nurseries of massive stars in our galaxy.

NGC 6334 – click for 1280×1280 image

More: here, here

Selected readings 4/28/10

2010-04-28T17:00:00.000-07:00

Interesting reading and news items.

These items are also bookmarked at my Diigo account.

Cross-discipline Effort Tracks Evolution of Human Uniqueness and Modern Behavior: A panel of scientists challenges what it is to be distinctly human and retraces the evolutionary steps that bipedal apes made to attain human traits. [Scientific American, 2/26/10]
Early Humans Used Brain Power, Innovation and Teamwork to Dominate the Planet: Scholars gathered to discuss how a unique combination of human traits helped our species survive to colonize the globe. [Scientific American, 2/27/10]
Mass of the Common Quark Finally Nailed Down: It’s not every day that scientists reduce the uncertainty in a fundamental constant of nature from 30% to 1.5%, but a team of theoretical physicists claims to have done just that. Using supercomputers and mind-bogglingly complex simulations, the researchers have calculated the masses of particles called “up quarks” and “down quarks” that make up protons and neutrons with 20 times greater precision than the previous standard. [ScienceNOW, 4/2/10]
Let’s draw Feynman diagrams!: There are few things more iconic of particle physics than Feynman diagrams. These little figures of squiggly show up prominently on particle physicists’ chalkboards alongside scribbled equations. ... The simplicity of these diagrams has a certain aesthetic appeal, though as one might imagine there are many layers of meaning behind them. The good news is that’s it’s really easy to understand the first few layers and today you will learn how to draw your own Feynman diagrams and interpret their physical meaning. [US LHC Blogs, 2/14/10]
More Feynman Diagrams: We could draw lines with arrows or wiggly lines and we were only permitted to join them using intersections (vertices) of the above form. These are the rules of the game. We then said that the arrowed lines are electrons (if the arrow goes from left to right) and positrons (if the arrow points in the opposite direction) while the wiggly lines are photons. The choice of rules is what we call a “model of particle interactions,” and in particular we developed what is called quantum electrodynamics, which is physics-talk for “the theory of electrons and photons.” [US LHC Blogs, 3/7/10]
QED + μ: introducing the muon: By now we’ve already familiarized ourselves with quantum electrodynamics (QED): the theory of electrons, positrons, and photons. Now we’re going to start adding on pieces to build up the Standard Model. We’ll start with the muon. [US LHC Blogs, 4/4/10]
Free will is an illusion, biologist says: When biologist Anthony Cashmore claims that the concept of free will is an illusion, he's not breaking any new ground. At least as far back as the ancient Greeks, people have wondered how humans seem to have the ability to make their own personal decisions in a manner lacking any causal component other than their desire to "will" something. But Cashmore, Professor of Biology at the University of Pennsylvania, says that many biologists today still cling to the idea of free will, and reject the idea that we are simply conscious machines, completely controlled by a combination of our chemistry and external environmental forces. [Physorg.com, 3/3/10]
Did the discovery of cooking make us human?: Cooking is something we all take for granted but a new theory suggests that if we had not learned to cook food, not only would we still look like chimps but, like them, we would also be compelled to spend most of the day chewing. [BBC News, 3/2/10]
Depression’s Upside: The mystery of depression is not that it exists — the mind, like the flesh, is prone to malfunction. Instead, the paradox of depression has long been its prevalence. While most mental illnesses are extremely rare — schizophrenia, for example, is seen in less than 1 percent of the population — depression is everywhere, as inescapable as the common cold. [New York Times, 2/25/10]
Human Culture, an Evolutionary Force: As with any other species, human populations are shaped by the usual forces of natural selection, like famine, disease or climate. A new force is now coming into focus. It is one with a surprising implication — that for the last 20,000 years or so, people have inadvertently been shaping their own evolution. [New York Times, 3/1/10]
Hogan’s noise: Cosmologist Craig Hogan, in contrast, has become enamored of a noise he claims is generated by something even tinier — a minuscule graininess in the otherwise smooth structure of spacetime. Call it Hogan’s noise. Many physicists are skeptical, but if his hunch about the existence of this subatomic clatter proves correct, it could have a mind-boggling implication: that the entire universe is nothing more than a giant hologram. [Science News, 3/13/10]
Hot tip: Target inflammation to ease obesity ills: What if you could be fat but avoid heart disease or diabetes? Scientists trying to break the fat-and-disease link increasingly say inflammation is the key. In the quest to prove it, a major study is under way testing whether an anti-inflammatory drug - an old, cheap cousin of aspirin - can fight the Type 2 diabetes spurred by obesity. And intriguing new research illustrates how those yellow globs of fat lurking under the skin are more than a storage site for extra calories. They're a toxic neighborhood where inflammation appears to be born. [Physorg.com, 3/1/10]
Protein folding: The dark side of proteins: Almost every human protein has segments that can form amyloids, the sticky aggregates known for their role in disease. Yet cells have evolved some elaborate defences. [Nature News, 4/7/10]
'Life as we don't know it' in the universe? Start with Titan.: From the dun plains of Meridiani on Mars to the "cool Jupiter" exoplanet CoRoT-9b circling a distant star in the constellation Serpens, scientists have put a premium on finding worlds that have the potential for liquid water, which enables life on Earth. But in Titan, scientists have found a world that, some suggest, could point to an exception to the rule. Might life exist without liquid water? Increasingly, Titan is becoming the focus of a movement to consider the possible existence of "life as we don't know it." [CSMonitor.com, 4/11/10]
Mirror Neurons - The unfalsifiable theory: I recently had the pleasure of giving a lecture on mirror neurons at UC San Diego which is a very active locale for folks working on the human mirror system. I expected a lot of push-back on my critical views of mirror neurons, and I wasn't disappointed. [Talking Brains, 3/19/10]
Explained: Radiative forcing: When people talk about global warming or the greenhouse effect, the main underlying scientific concept that describes the process is radiative forcing. [Physorg.com, 3/10/10]
Explained: Climate sensitivity: Climate sensitivity is the term used by the Intergovernmental Panel on Climate Change (IPCC) to express the relationship between the human-caused emissions that add to the Earth's greenhouse effect -- carbon dioxide and a variety of other greenhouse gases -- and the temperature changes that will result from these emissions. [Physorg.com, 3/19/10]
Did Society Do It?: Language seems unlikely to have started as the solution to any one problem. Evolution can handle any single task with a more focused adaptation. There seems no reason to doubt that early Homo did use proto-speech for referring to absent things and for recruiting, but there also seems no reason to suppose it was limited to that role. [Babel's Dawn, 4/11/10]
How robots think: an introduction: In the 1960's, researchers in artificial intelligence were boldly declaring that we'd have thinking machines fully equivalent to humans in 10 years. Instead, for most of the past half-century, the only robots we saw outside of movies and labs were arms confined to factory floors and were remotely operated by humans. Building machines that behaved intelligently in the real world was harder than anyone imagined. [Nobel Intent, 3/15/10]
Hunt for the sterile neutrino heats up: Neutrinos like to keep to themselves. These ghostly particles are so reluctant to interact with ordinary matter that billions zip harmlessly through each person every day, and it takes giant, specialized detectors to capture even a handful of them. Now astronomers are finding hints of an even more elusive type of neutrino, one so shy that it could never be detected directly: the sterile neutrino. [Nature News, 3/17/10]
Explained: Regression analysis: Regression analysis. It sounds like a part of Freudian psychology. In reality, a regression is a seemingly ubiquitous statistical tool appearing in legions of scientific papers, and regression analysis is a method of measuring the link between two or more phenomena. [Physorg.com, 3/16/10]
A Skeptic Questions Cancer Genome Projects: Vogelstein summed up by saying that cancer has gone from "a complete black box" to something that "we really kind of understand." The "sobering" part, he said, is that he doesn't expect there will be many new genes or genetic breakthroughs. He has pinned his own hopes for preventing cancer deaths on using genetics to diagnose cancers early, when they're more treatable. [ScienceInsider, 4/23/10]
Bigger, Better Space Telescopes Following In Hubble's Footsteps: Hubble Space Telescope huggers are celebrating the iconic observatory's 20th birthday, even as scientists anticipate the next generation of bigger and more powerful successors to the famed orbital instrument. [Space.com, 4/23/10]
What Is Mathematics For? [PDF]: What mathematics education is for is not for jobs. It is to teach the race to reason. It does not, heaven knows, always succeed, but it is the best method that we have. It is not the only road to the goal, but there is none better. [Notices of the AMS, 4/27/10]
When multi-tasking, each half of the brain focuses on different goals: The part of our brain that controls out motivation to pursue our goals can divide its attention between two tasks. The left half devotes itself to one task and the right half to the other. This division of labour allows us to multi-task, but it also puts an upper limit on our abilities. [Not Exactly Rocket Science, 4/15/10]
To sleep, perchance to dream, perchance to remember: The last decade of research has clearly shown that sleep is one of the best aide memoires that we have. During this nightly time-out, our brain can rehearse information that it has picked up during the day and consolidate them into lasting memories. Wamsley’s new study supports that idea but it also shows that dreaming while you nap can strengthen our memories even further. [Not Exactly Rocket Science, 4/22/10]
The Utrecht Paradigm: There is something wrong here. If you began stopping people on the street and asked them if they thought it likely that language depends on a mixture of biological adaptations and cultural innovations, wouldn’t the first 999 out of 1000 answer yes? So what kind of knot can language scholars have tied themselves into for the news out of Utrecht to be that they too would answer yes? But that’s the case, although it looks temporary and unsustainable. [Babel's Dawn, 4/25/10]

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