Originally posted on sciy.org by Ron Anastasia on Thu 07 Dec 2006 12:07 PM PST
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Whole Black Hole Meal Observed SPACE.COM Staff posted: 06 December 2006 02:25 pm ET |
Scientists
have captured [image]
for the first time the entire process of a black hole eating a stellar meal.
An orbiting
telescope called Galaxy Evolution Explorer, detected bright ultraviolet flares emitted
from a star that had ventured too
close to the hungry
void of a black hole and began to plunge into it.
"This
type of event is very rare, so we are lucky to study the entire process from
beginning to end," said Suvi Gezari of the California Institute of
Technology.
For
thousands of years, this black hole most likely rested quietly deep inside an
unnamed galaxy before the
opportunity for a filling feast came up.
Today, the
space-based telescope continues to periodically watch this ultraviolet light fade
as the black hole finishes the remaining bits of its meal.
“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 Christopher
Martin also of the California Institute of Technology.
In the
early 1990s, three other dormant black holes were suspected of having eaten
nearby stars when satellites picked
up X-ray
flares from their host galaxies.
Only with
better technology and a decade later were astronomers able to confirm that the
black holes' X-rays had faded dramatically—a sign that stars were swallowed.
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 at the center of the Milky Way,
hardly make a peep, so they are difficult to study.
It’s rare
for an unsuspecting star to wander too close to a dormant black hole. Such an
event is thought to occur about once every 10,000 years in a typical galaxy.
A star will flatten and stretch apart when gravity from a nearby black hole overpowers 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," Gezari said. "Now that we
know we can observe these events with ultraviolet light, we've got a new tool
for finding more."
The
findings are reported in the Dec. 10 issue of Astrophysical Journal Letters.
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