Supermassive
Black Hole Mashes Up and Consumes a Star
December 5th, 2006
A supermassive
black hole in a distant galaxy has been caught in the act of consuming a
star. In fact, NASA’s Galaxy Evolution Explorer was able to watch the entire
process, from the beginning to the end. A some point in the recent past,
a star got too close to the supermassive black hole, and was torn apart.
The shreds swirled around the black hole, and the Galaxy Evolution Explorer
spotted the bright blast of ultraviolet light.
Artist illustration
of a black hole. Image credit: NASA/JPL
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 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 Röntgen 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 verdana as massive as
our sun. Its host galaxy is located 4 billion light-years away in the Bootes
constellation.
An artist’s
concept and additional information about the Galaxy Evolution Explorer is
online at http://www.nasa.gov/galex/
.
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.
Original
Source: NASA/JPL
News Release
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