Whole Black Hole Meal Observed

Whole Black Hole Meal Observed
The artist's concept chronicles a star being ripped apart and swallowed by a supermassive black hole over time. First, the intact sun-like star (left) ventures too close to the black hole, and its own self-gravity is overwhelmed by the black hole's gravity. The star then stretches apart (middle yellow blob) and eventually breaks into stellar crumbs, some of which swirl into the black hole (cloudy ring at right). This doomed material heats up and radiates light, including ultraviolet light, before disappearing forever into the black hole. The Galaxy Evolution Explorer was able to watch this process unfold by observing changes in ultraviolet light.
(Image: © NASA/JPL-Caltech)

Scientistshave captured [image]for the first time the entire process of a black hole eating a stellar meal.

An orbitingtelescope called Galaxy Evolution Explorer, detected bright ultraviolet flares emittedfrom a star that had ventured tooclose to the hungryvoid of a black hole and began to plunge into it.

"Thistype of event is very rare, so we are lucky to study the entire process frombeginning to end," said Suvi Gezari of the California Institute ofTechnology.

Forthousands of years, this black hole most likely rested quietly deep inside anunnamed galaxy before theopportunity for a filling feast came up.

Today, thespace-based telescope continues to periodically watch this ultraviolet light fadeas the black hole finishes the remaining bits of its meal.

"This willhelp us greatly in weighing black holes in the universe, and in understanding howthey feed and grow in their host galaxies as the universe evolves," said ChristopherMartin also of the California Institute of Technology.

In theearly 1990s, three other dormant black holes were suspected of having eatennearby stars when satellites pickedup X-rayflares from their host galaxies.

Only withbetter technology and a decade later were astronomers able to confirm that theblack holes' X-rays had faded dramatically--a sign that stars were swallowed.

Black holesare heaps of concentrated matter whose gravity is so strong that even lightcannot escape. Supermassive black holes are believed to reside at the cores ofevery galaxy, though some are thought to be more active than others.

Activeblack holes drag surrounding material into them, heating it up and causing itto 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 rarefor an unsuspecting star to wander too close to a dormant black hole. Such anevent is thought to occur about once every 10,000 years in a typical galaxy.

A star willflatten and stretch apart when gravity from a nearby black hole overpowers itsown self-gravity. The same phenomenon happens on Earth every day, as the moon'sgravity tugs on our world, causing the oceans to rise and fall.

Once a starhas been disrupted, a portion of its gaseous body will then be pulled into the blackhole and heated up to temperatures that emit X-rays and ultraviolet light.

"Thestar just couldn't hold itself together," Gezari said. "Now that weknow we can observe these events with ultraviolet light, we've got a new toolfor finding more."

Thefindings are reported in the Dec. 10 issue of Astrophysical Journal Letters.

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