Saturday, October 21, 2006

Black holes in the news

No, this isn't metaphorically about censorship in the news media. It's about real black holes.

There's been a lot of new information coming out about black holes recently – some of which we're already discussed, such as this and this. (There's more if you search the archives.)

And just think – only a few years ago many astrophysicists weren't convinced that black holes (as usually conceived) really existed. A few are even still trying to come up with alternative explanations (e. g. here, here, here). Whatever.

Here are a few more news items, and that's not even getting into news about quasars and the effect of supermassive black holes on star birth – which we'll talk about separately.

Scientists Nudge Closer To The Edge Of A Black Hole
NASA scientists and their international partners using the new Japanese Suzaku satellite have collected a startling new set of black hole observations, revealing details of twisted space and warped time never before seen with such precision.

The observations include clocking the speed of a black hole's spin rate and measuring the angle at which matter pours into the void, as well as evidence for a wall of X-ray light pulled back and flattened by gravity

Another one:

Chandra reviews black hole musical: Epic but off-key
A gigantic sonic boom generated by a supermassive black hole has been found with NASA's Chandra X-ray Observatory, along with evidence for a cacophony of deep sound.

This discovery was made by using data from the longest X-ray observation ever of M87, a nearby giant elliptical galaxy. M87 is centrally located in the Virgo cluster of galaxies and is known to harbor one of the Universe's most massive black holes.

Scientists detected loops and rings in the hot, X-ray emitting gas that permeates the cluster and surrounds the galaxy. These loops provide evidence for periodic eruptions that occurred near the supermassive black hole, and that generate changes in pressure, or pressure waves, in the cluster gas that manifested themselves as sound.

"We can tell that many deep and different sounds have been rumbling through this cluster for most of the lifetime of the Universe," said William Forman of the Harvard-Smithsonian Center for Astrophysics (CfA).

The outbursts in M87, which happen every few million years, prevent the huge reservoir of gas in the cluster from cooling and forming many new stars. Without these outbursts and resultant heating, M87 would not be the elliptical galaxy it is today.

The next item has a little more about the "iron K-alpha" spectroscopic line that's mentioned in the previous article:

Astronomers use supercomputers to study atoms linked to black holes
The atom that most black-hole hunters are interested in is iron, and that's where Einstein's general theory of relativity comes in.

The immense gravity of a black hole should, according to relativity, distort the X-ray signal as seen from Earth, particularly for iron atoms. The signal is a spectrum, and looks like a series of lines, with each atom having its own line. One line in particular, called the iron K-alpha line, appears broadened for X-rays emanating from the center of active galaxies, and it is often cited as a key indication of a black hole.

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