The galactic center is the "downtown" of the Milky Way, a place bathed in a fog of superheated gas and extremely active with stars being born, old stars blowing up into supernovae and black holes sucking in clouds of matter, said Q. Daniel Wang of the University of Massachusetts.

"The center of the galaxy is where the action is," Wang said at the national meeting of the American Astronomical Society.

The center of the Milky Way is obscured by a dense screen of dust, gas and the glare of millions of stars. The solar system, which includes the Earth and the sun, is in the "suburbs" of Milky Way, about half way out one of the galaxy's spiral arms and about 25,000 light years from the center. As a result, astronomers have been unable to get a clear picture of the center using ordinary telescopes.

But X-rays generated by the churning energy at the center penetrate the dust. The Chandra X-Ray Observatory, launched in 1999, has been able to take a series of 30 pictures that are combined to provide the clearest portrait of the galactic center ever taken. The mosaic portrait covers an area 400 light years high and some 900 light years long. A light year is about six trillion miles.

Wang, who supervised the project, said the portrait captures more than a thousand X-ray sources. Earlier X-ray telescopes detected only about a dozen, he said.

"This is the big city of stars," said Wang. "What happens there matters to the rest of the galaxy."

He said the galactic center is bathed in a fog of gas heated to about 10 million degrees.

"The gas is hot, but not as hot as we previously believed," said Wang. Earlier studies had estimated the gas at about 100 million degrees.

By analyzing the spectra of the X-rays, he said, his team was able to determine that the galactic center has hundreds of white dwarf stars, which are hot, faint stars. There also are neutron stars, the collapsed husk of a medium stars and a powerful source of X-rays, and stellar black holes, a massive star that has collapsed into a point of such density that not even light can escape.

And at the very center, said Wang, is a super-massive black hole, a single point with the density of millions of suns and the gravitational center of the Milky Way.

Wang said the Milky Way center is in a constant roar of star formation and destruction.

"This is the most active region in our galaxy," said Wang.

By studying the Milky Way center with pictures from Chandra, Wang said astronomers will learn the specific details about the general life of galaxies, how they make stars and how they distribute the basic elements that are made in stars.

Wang said the torrid gas at the center seems to circulate outward, cooling on the edges of the galaxy and then streaming back in. This gas could be carrying and distributing throughout the galaxy many of the heavier elements, such as carbon, that were made in stars, he said.

Another astronomer, Farhad Yusef-Zaden of Northwestern University, said Wang's pictures from Chandra are giving details that never before were possible, but he said it is too early to draw any conclusions about galaxies. He said it will takes years of analysis to fully understand all that is happening in the Milky Way center.

"These are very pretty pictures," said Yusef-Zaden, "but the real work is just beginning."

On the net:

Chandra images: http://www.chandra.harvard.edu

Also: http://chandra.nasa.gov

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