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Title:  'Supermassive' Black Hole Found in the Center of our Galaxy
Date:    September 7, 1998



Media contact:                       Embargoed until 1 P.M., EST
Greg Lester                                    September 7, 1998
(703) 306-1070/glester@nsf.gov                      NSF PR 98-47

Program contact:
Terry Oswalt
(703) 306-1825/toswalt@nsf.gov

   `SUPERMASSIVE' BLACK HOLE FOUND IN THE CENTER OF OUR GALAXY

     The presence of an enormous black hole at the center of our
galaxy has been detected by a researcher funded, in part, by the
National Science Foundation (NSF).  The evidence will be reported
today at the Central Parsecs Galactic Center Workshop '98 in
Tucson, Arizona, by Andrea Ghez, of the University of California
Los Angeles.

     "What lies in the center of the Milky Way has been one of
this century's `big' science questions," said Terry Oswalt, NSF
program manager for Stellar Astronomy and Astrophysics.  "Ghez's
work has massive implications on our understanding of how
galaxies evolve."

     Black holes are formed from the remnants of collapsed stars.
A black hole consists of a large mass compacted so densely that
not even light can escape its force of gravity.  Since Ghez could
not directly see a black hole, she inferred its presence by
searching for the gravitational influence it imposes on nearby
objects she could see, namely stars.

     In 1995, using the Keck I Telescope atop Mauna Kea in
Hawaii, Ghez began tracking the movement of 200 stars near the
galactic center.  She found at least 20 stars that exhibited the
telling signs of influence by extreme gravitational forces.

     These stars are spiraling around the black hole at speeds of
up to three million miles per hour_about 10 times the speed at
which stars typically move.  In order to account for the rapid
speeds of these stars, Ghez determined that an object 2.6 million
times more massive than our Sun must be concentrated into a
single black hole.

     Just getting a clear view of the center of our galaxy is an
impressive feat in itself.  To overcome the distortion created by
the Earth's atmosphere, Ghez made her observations using a
technique called "infrared speckle interferometry."  The
procedure, which she helped develop, uses computers to analyze
thousands of high-speed, high-resolution snapshots.

     The result: an image that has at least 20 times better
resolution than those made by traditional earthbound imaging
techniques.  "It's like putting on glasses," said Ghez.

     Using this technique in 1995, Ghez witnessed the
disappearance of a star that was, at the time, the closest object
to the black hole.  Whether the star was sucked into the black
hole, or simply went behind it, scientists may never know.

     But we have little to fear about a similar fate for Earth,
since the center of the Milky Way galaxy is approximately 24,000
light years away.  Because of the Earth's position on an outer
arm of the spiraling Milky Way, much of our knowledge about
galaxies does not come from our own.  Ghez's research, however,
gives us a definitive view about a part of Galaxy that we have
never seen before.

     "There is an incredible amount of matter between us and the
center of the Milky Way to obscure our view," said Oswalt.  "Ghez
has pulled the living room shades open a bit and finally given us
a good look at what's going on in our own backyard."

                              -NSF-

The Central Parsecs Galactic Center Workshop '98, is being held
in Tucson, Arizona from September 7 to 11. For more information,
contact Alaina Levine at (520) 621-4969, or visit the website at:
http://www.mpifr-bonn.mpg.de/gc98