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.
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.