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NSF PR 98-47 - September 7, 1998
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'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 our own 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."
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
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