Saturday, February 11, 2006

207th AAAS meeting

The American Astronomical Society holds two main meetings a year, at which major research findings are announced and presented. The most recent meeting, the 207th, was held in Washington, DC January 8 through 12.

This meeting had an unusually large number of especially interesting research presentations, or so it seems to me. They cover a wide range of topics in astronomy, planetary science, astrophysics, cosmology -- as you would expect.

I'm just going to list very briefly some of what seem to be the most significant results. As time permits (ha!) I'll try to write more in depth about some of these.

Black holes

Although black holes have been discussed as a hypothetical possibility for decades, it's only been within about the past five years that pretty good evidence has been obtained for the actual existence of black holes. The evidence continues to grow more substantial and more detailed. One study investigated the internal motions of gas surrounding the nucleus of the active galaxy NGC 1097. It was able to track the gas to within about 10 light-years of the central black hole of NGC 1097. Reference: Scientists Probe Black Hole’s Inner Sanctum.

Another study compared neutron stars and (apparent) black holes using NASA's Rossi X-ray Timing Explorer. X-ray emissions from the vicininty of the two kinds of objects behave quite differently. Those from near a black hole are what would be expected from a black hole event horizon into which matter falls without a trace. Reference: Scientists find black hole's 'point of no return'.

Like just about all other known spiral galaxies, the Milky Way contains a supermassive black hole at its center. This location has been identified with the region known as Sagittarius A*. A study using both ground- and space-based telescopes has found rapid flares close to the innermost region of the black hole in many different wavelengths and that these emissions go up and down together. Reference: Astronomers shed surprising light on our galaxy's black hole.

A team of astronomers has observed a region less than 100 miles from the event horizon of a spinning black hole system called GRO J1655-40. They documented the existence of periodic fluctuations, at predictable frequencies, of X-ray emissions from that region. Reference: Spinning black hole leaves dent in space-time.

Galaxies and their central black holes

Several years ago it became clear that there is a rough correlation between the size of a galaxy (especially the central bulge of a spiral galaxy) and the size of the central black hole that seems to be almost always there. In 2004 the Hubble Space Telescope completed (after about 115 days) a single image of some of the farthest -- and consequently youngest -- visible galaxies in the universe. Careful examination of this image -- called the Hubble Ultra Deep Field -- now reveals details of how those young galaxies developed at an early age. Galaxies grow simply by merging with their nearest neighbors. And at the same time, the central black hole in the merged galaxy grows by consuming stars, dust, and gas that has been swept up during the merger. Reference: Monster Black Holes Grow After Galactic Mergers

One of the most intriguing questions about supermassive black holes is how they get started in the first place, before they begin to grow by accretion. Are they remnants of enormous stars that formed in the early universe and then exploded as supernovae? Or did they coalesce directly out of especially dense regions of matter in the early universe? The initial stage of a supermassive black hole is simply a black hole of intermediate mass. But examples of such intermediate mass objects are difficult to find, since they have grown substantially over time unless they are rather young. Now a careful study of data from the Sloan Digital Sky Survey has turned up 19 black holes with masses less than one million solar masses -- which qualifies as merely "intermediate" size. Young intermediate mass black holes are in effect mini-quasars that produced enormous quantities of energy as they consumed infalling matter. Consequently, they may have played an important role during the period of re-ionization of the universe several hundred years after the big bang. Reference: Growing Supermassive Black Holes from Seeds.

Dark matter galaxy

Dark matter galaxies, consisting entirely of dark matter and hydrogen gas but with no visible stars, have been reported before. (Here, for example.) Now another cloud of hydrogen gas, called VIRGOHI 21, at a distance of 50 million light-years in the Virgo Cluster, has been identified by radio telescope studies as a dark matter galaxy, since its total mass appears to be 100 times as large as accounted for by the hydrogen. The total mass is 10 billion solar mass units, even though there are no visible stars. Reference: New evidence for a Dark Matter Galaxy.

Warping and vibration of the Milky Way produced by dark matter

The Milky Way, apparently like all galaxies, is enveloped in a cloud of dark matter that is much more massive than the visible galaxy itself. It has also been known that the galaxy warps and vibrates like a limp pizza. A computer model has shown that this distortion of the Milky Way can be explained by movement of the two main satellite galaxies (the Large and Small Magellanic Clouds) through the dark matter. This represents yet more evidence that dark matter is real, even though we still don't know what it is. Reference: Milky Way galaxy is warped and vibrating like a drum.

High-energy source of X-rays and gamma-rays

It's been known for years that there is an source of very high-energy X-rays and gamma-rays inside our galaxy. Now that source has been identified as a very massive star cluster, about 20 times as massive as the average cluster. It contains 14 relatively rare red supergiant stars. Reference: Mystery Solved: High-Energy Fireworks Linked to Massive Star Cluster.

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To be continued... there's much more

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