Dolores Beasley
Headquarters, Washington                      Jan. 9, 2002
(Phone: 202/358-1753)

Steve Roy
Marshall Space Flight Center, Huntsville, Ala.
(Phone: 256/544-6535)

Megan Watzke
Chandra X-ray Observatory Center, Cambridge, Mass.
(Phone: 617/496-7998)

RELEASE: 02-03

CHANDRA TAKES IN BRIGHT LIGHTS, BIG CITY OF MILKY WAY

     NASA's Chandra X-ray Observatory has made a stunning, 
high-energy panorama of the central regions of our Milky Way 
galaxy. The findings are an important step toward 
understanding the most active area of the Milky Way as well 
as other galaxies throughout the universe.

Like a sprawling megalopolis, the new Chandra images show 
hundreds of white dwarf stars, neutron stars and black holes 
bathed in an incandescent fog of multimillion-degree gas 
around a supermassive black hole. 

"The center of the galaxy is where the action is," said Q. 
Daniel Wang of the University of Massachusetts, Amherst. 
"With these images, we get a new perspective of the interplay 
between stars, gas and dust, as well as the magnetic fields 
and gravity in the region. We can see how such forces affect 
the immediate vicinity and may influence other aspects of the 
galaxy." 

Wang presented the montage of 30 separate Chandra images 
today at the American Astronomical Society meeting in 
Washington, and in a paper published in the Jan. 10, 2002, 
issue of the journal Nature. The images, made with the 
Advanced CCD Imaging Spectrometer (ACIS) July 16-21, 2001, 
covered a 400- by 900-light-year swath of the center of the 
galaxy. 

One immediate result was that the team could separate out the 
individual X-ray sources from the diffuse glow produced by 
hot gas. "We can now see that the sources are responsible for 
most of the X-rays from highly ionized iron previously 
attributed to the diffuse glow," said Eric Gotthelf, of 
Columbia University in New York, a co-author. "So we must now 
revise our notion of the hot gas, which appears to be about 
10 times cooler than previously thought. It's only a 
relatively mild 10 million degrees!" 

The diffuse X-ray emission seems to be related to the turmoil 
and density of matter in the inner Milky Way. Stars are 
forming there at a much more rapid rate than in the galactic 
"suburbs." Many of the most massive stars in the galaxy are 
located in the galactic center and are furiously boiling off 
their outer layers in searing stellar winds. Supernova 
explosions are far more common in the region and send shock 
waves booming through the inner galaxy. 

And then there is the three-million-solar-mass black hole at 
the epicenter. Although Chandra recently observed a small 
flare from the vicinity of the central supermassive black 
hole, the power output near the black hole remains relatively 
low. 

However, an unexplained fluorescence of iron atoms, observed 
by the team to be associated with molecular clouds a few 
hundred light-years away, may indicate that the supermassive 
black hole was hundreds of times brighter in the past. 
Alternatively, the fluorescence could be due to high-energy 
particles called cosmic rays produced by supernovae or bygone 
eruptions from the supermassive black hole. 

"The galactic center is dominated by very high pressures due 
to the hot gas component and the strong magnetic fields," 
said Cordelia Lang, also of the University of Massachusetts, 
and a co-author. "It's a nice place to visit with a telescope 
but I wouldn't want to live there."

The Chandra map shows that the high-pressure and high-
temperature gas is apparently escaping from the center into 
the halo of the galaxy. "A galaxy is a sort of ecosystem, and 
the activity in the center can seriously affect the evolution 
of the galaxy as a whole," said Wang. "Astronomically, the 
center of the Milky Way is really in our backyard, and, 
therefore, provides an excellent laboratory to learn about 
the cores of other galaxies."

The ACIS instrument was developed for NASA by Pennsylvania 
State University, University Park, and Massachusetts 
Institute of Technology, Cambridge. NASA's Marshall Space 
Flight Center in Huntsville, Ala., manages the Chandra 
program, and TRW, Inc., Redondo Beach, Calif., is the prime 
contractor. The Smithsonian's Chandra X-ray Center controls 
science and flight operations from Cambridge, Mass.

More information on Chandra and images associated with this 
release are available at: 
http://chandra.harvard.edu
and
http://chandra.nasa.gov
                               -end-