Center of the Galaxy - Observations from Chandra

[Astronuc]

Chandra turns up the heat in the Milky Way's center

This image was produced by combining a dozen NASA Chandra X-ray Observatory observations made of a 130 light-year region in the center of the Milky Way. The colors represent low (red), medium (green) and high (blue) energy X-rays. Thanks to Chandra's unique resolving power, astronomers have now been able to identify thousands of point-like X-ray sources due to neutron stars, black holes, white dwarfs, foreground stars, and background galaxies. What remains is a diffuse X-ray glow extending from the upper left to the lower right, along the direction of the disk of the galaxy.

The spectrum of the diffuse glow is consistent with a hot gas cloud that contains two components: 10-million-degree Celsius gas and 100-million-degree gas. The diffuse X-rays appear to be the brightest part of a ridge of X-ray emission that stretches for several thousand light years along the disk of the Galaxy. The extent of this ridge implies that the diffuse hot gas in this image is probably not being heated by the supermassive black hole at the center of the Milky Way.

Shock waves from supernova explosions are the most likely explanation for heating the 10-million-degree gas, but how the 100-million-degree gas is heated is not known. Ordinary supernova shock waves won't work, and heating by very high-energy particles produces the wrong spectrum of X-rays. Also, the observed galactic magnetic field appears to rule out confinement and heating by magnetic turbulence.

It is possible that the high-energy X-ray component of the hot gas only appears to be diffuse, and is in fact due to the combined glow of an as yet undetected population of point-like sources, like the diffuse lights of a city seen at a great distance. The difficulty with this explanation is that 200,000 sources would be required in the observed region. Such a large unresolved population of sources would produce a much smoother X-ray glow than is observed. Furthermore, there is no known class of objects that could account for such a large number of high-energy X-ray sources in the center of the Milky Way.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program. (NASA/CXC/UCLA/M. Muno et al.)

http://www.msfc.nasa.gov/news/news/photos/2004/photos04-169.html (jps available)

[Astronuc]

Big stars are born near Milky Way's black hole

By Deborah Zabarenko (Reuters on Yahoo)

WASHINGTON (Reuters) - Dozens of massive stars, destined for a short but brilliant life, were born less than a light-year away from the Milky Way's central black hole, one of the most hostile environments in our galaxy, astronomers reported on Thursday.

On Earth, this might be a bit like setting up a maternity ward on the side of an active volcano. But researchers using the Chandra X-ray Observatory and other instruments believe there is a safe zone around black holes, a big dust ring where stars can form.

Black holes, including the one at the center of our galaxy, are monstrous matter-sucking drains in space, with gravitational pull so strong that nothing, not even light, can escape once it comes within the hole's grasp.

These young stars, however, are just far enough away to be held in orbit around the hole much as planets are kept in orbit around the sun, according to Sergei Nayakshin of the University of Leicester, United Kingdom.

At less than a light-year's distance, the 50 or 100 massive young stars are quite close to the black hole, but not close enough to be drawn in, Nayakshin said in a telephone interview.

A light-year is about 6 trillion miles, the distance light travels in a year. By comparison, Earth is about 26,000 light-years from the galactic center where the black hole lies.

http://news.yahoo.com/s/nm/20051013/ts_nm/space_hole_dc
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Spaceref.com - NASA'S Chandra X-Ray Observatory Reveals New Star Generation
http://www.spaceref.com/news/viewpr.html?pid=18036

The stars, orbiting less than a light year from the Milky Way's central black hole, are known as Sagittarius A* ( Sgr A*). At such close distances to Sgr A*, the standard model for star forming gas clouds predicts they should have been ripped apart by tidal forces from the black hole. Two models, based on previous research, to explain this puzzle have been proposed. In the disk model, the gravity of a dense disk of gas around Sgr A* offsets the tidal forces and allows stars to form.  

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Top Photo (Reuters) This light-year mosaic of several observatory images of the central region of our Milky Way galaxy reveals hundreds of white dwarf stars, neutron stars, and black holes bathed in an incandescent fog of multimillion-degree gas. A supermassive black hole at the center of the Galaxy is located inside the bright white patch in the center of the image. Dozens of massive stars, destined for a short but brilliant life, were born less than a light-year away from the Milky Way's central black hole, one of the most hostile environments in our galaxy, astronomers reported on Thursday. REUTERS/NASA

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Bottom photo - Chandra's image of the Galactic Center (left) has provided evidence for a new and unexpected way for stars to form. A combination of infrared and X-ray observations indicates that a surplus of massive stars has formed from a large disk of gas around Sagittarius A*, the Milky Way's central black hole (illustration on right).

from http://chandra.harvard.edu/photo/2005/sgra/
Sagittarius A*: Stars Surprisingly Form in Extreme Environment Around Milky Way's Black Hole
and http://chandra.harvard.edu/press/05_releases/press_101305.html