ASHINGTON - The sharpest picture ever taken
of the center of the Milky Way galaxy, home of the solar system, shows a
cast of bizarre stellar characters - neutron stars, dwarf stars, and small
black holes - clustered around a super-massive black hole.
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-Amherst.
''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 the Milky Way, about halfway
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 6 trillion miles.
Wang, who supervised the project, said the portrait captures more than
1,000 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.
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.''
.gif){kind=spacer}
