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NASA
Telescope Sees Black Hole Munch on a Star
12.05.06
A giant black hole has been caught red-handed dipping
into a cosmic cookie jar of stars by NASA's Galaxy Evolution
Explorer. This is the first time astronomers have seen the whole
process of a black hole eating a star, from its first to nearly
final bites.
This
artist's concept shows a supermassive black hole at the
center of a remote galaxy digesting the remnants of a star.
More
Information ROLLOVER
Credit:
NASA/JPL-Caltech
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"This type of event is
very rare, so we are lucky to study the entire process from
beginning to end," said Dr. Suvi Gezari of the California
Institute of Technology, Pasadena, Calif. Gezari is lead author
of a new paper appearing in the Dec. 10 issue of Astrophysical
Journal Letters.
For perhaps thousands of years, the
black hole rested quietly deep inside an unnamed elliptical
galaxy. But then a star ventured a little too close to the
sleeping black hole and was torn to shreds by the force of its
gravity. Part of the shredded star swirled around the black hole,
then began to plunge into it, triggering a bright ultraviolet
flare that the Galaxy Evolution Explorer was able to detect.
Today, the space-based telescope continues to
periodically watch this ultraviolet light fade as the black hole
finishes the remaining bits of its stellar meal. The observations
will ultimately provide a better understanding of how black holes
evolve with their host galaxies.
"This will help us
greatly in weighing black holes in the universe, and in
understanding how they feed and grow in their host galaxies as
the universe evolves," said Dr. Christopher Martin of
Caltech, a co-author of the paper and the principal investigator
for the Galaxy Evolution Explorer.
In the early 1990s,
three other resting, or dormant, black holes were suspected of
having eaten stars when the joint German-American-British R?ntgen
X-ray satellite picked up X-ray flares from their host galaxies.
Astronomers had to wait until a decade later for NASA's Chandra
X-ray Observatory and the European Space Agency's XMM-Newton
X-ray observatory to confirm those findings, showing that the
black holes' X-rays had faded dramatically -- a sign that stars
were swallowed.
Now, Gezari and her colleagues have, for
the first time, watched a similar feeding frenzy unfold, as it
happens, through the ultraviolet eyes of the Galaxy Evolution
Explorer. They used the telescope's detectors to catch an
ultraviolet flare from a distant galaxy, then watched the flare
diminish over time, as the galaxy's central black hole consumed
the star. Additional data from Chandra, the Canada France Hawaii
Telescope in Hawaii and the Keck Telescope, also in Hawaii,
helped the team chronicle the event in multiple wavelengths over
two years.
Black holes are heaps of concentrated matter
whose gravity is so strong that even light cannot escape.
Supermassive black holes are believed to reside at the cores of
every galaxy, though some are thought to be more active than
others. Active black holes drag surrounding material into them,
heating it up and causing it to glow. Dormant black holes, like
the one in our Milky Way galaxy, hardly make a peep, so they are
difficult to study.
That's why astronomers get excited
when an unsuspecting star wanders too close to a dormant black
hole, an event thought to happen about once every 10,000 years in
a typical galaxy. A star will flatten and stretch apart when a
nearby black hole's gravity overcomes its own self-gravity. The
same phenomenon happens on Earth every day, as the moon's gravity
tugs on our world, causing the oceans to rise and fall. Once a
star has been disrupted, a portion of its gaseous body will then
be pulled into the black hole and heated up to temperatures that
emit X-rays and ultraviolet light.
"The star just
couldn't hold itself together," said Gezari, adding, "Now
that we know we can observe these events with ultraviolet light,
we've got a new tool for finding more."
The newfound
feeding black hole is thought to be tens of millions times as
massive as our sun. Its host galaxy is located 4 billion
light-years away in the Bootes constellation.
The
California Institute of Technology in Pasadena, Calif., leads the
Galaxy Evolution Explorer mission and is responsible for science
operations and data analysis. NASA's Jet Propulsion Laboratory,
also in Pasadena, manages the mission and built the science
instrument. The mission was developed under NASA's Explorers
Program managed by the Goddard Space Flight Center, Greenbelt,
Md. Researchers sponsored by Yonsei University in South Korea and
the Centre National d'Etudes Spatiales (CNES) in France
collaborated on this mission.
Source
/ Credit: NASA / JPL
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