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In a galaxy far, far away. . . An artist's illustration showing a massive black hole in a
galaxy more than 4 billion light-years away digesting the remnants of a star. (Image
courtesy of NASA/JPL-Caltech)
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Black Hole Gobbles Up Remote Star
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A giant black hole has been observed swallowing a star by NASA's Galaxy
Evolution Explorer. It's the first time astronomers have seen the whole
process from beginning to end of a black hole eating a star.
The black hole had rested quietly deep inside an unnamed elliptical galaxy for
perhaps thousands of years. 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.
"The star just couldn't hold itself together," Dr. Suvi Gezari of the California
Institute of Technology said in describing the event in Astrophysical Journal
Letters.
"Now that we know we can observe these events with ultraviolet light, we've
got a new tool for finding more," he added.
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.
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.
In the early 1990s, three other resting, or dormant, black holes were
suspected of having eaten stars when a joint German-American-British 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.
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