Black Hole Found Choking on Massive Meal of Stardust
Astrophysicists at MIT have gained new insight into the energy that radiates from a feeding black hole as it tears apart a nearby star.
Indigestion is no small matter for a black hole. The energy from a belching black hole radiates across the electromagnetic spectrum, emitting everything from radio waves to gammas, but the infrequent outbursts are hard to spot.
Such outbursts, known as tidal disruption flares, occur when a star wanders too close to a black hole and is torn apart by the cosmic phenomenon's immense gravitational force.
Astrophysicists at the Massachusetts Institute of Technology recently announced that they had gained new insight into the energy emitted by this stellar ingestion. It all began on Nov. 11, 2014, when a global network of robotic telescopes spotted a flare in a galaxy nearly 300 million light years from Earth.
The All-Sky Automated Survey for SuperNovae, or ASASSN, sent out a notice. Astronomers quickly aimed an armada of telescopes at the flare, named ASASSN-14li, and collected data for 270 days.
They discovered a pattern: bursts of radiation, followed by dips and then another set of bursts. The identical fluctuations were found first in optical light collected by Las Cumbres Observatory Global Telescope and then in X-rays detected by Swift, NASA's orbiting space observatory.
"Only recently have telescopes started 'talking' to each other, and for this particular event we were lucky because a lot of people were ready for it," MIT astrophysicist Dheeraj Pasham said in a statement. "It just resulted in a lot of data."
Feeding the data into computer models, Pasham and his colleagues discovered a curious phenomenon.
As the black hole ripped apart its stellar meal, debris from the star collided with itself, creating flares in optical light at the collision sites. Days later, as the debris swirled closer to the black hole and heated up, it flared again, this time in higher-energy X-ray light.
The debris then disappeared into the black hole, an object so dense with matter that not even light can escape its gravitational grasp.
"In essence, this black hole has not had much to feed on for a while, and suddenly along comes an unlucky star full of matter," Pasham said. "This stellar material is not just continuously being fed onto the black hole, but it's interacting with itself - stopping and going, stopping and going. This is telling us that the black hole is 'choking' on this sudden supply of stellar debris."
Typically, supermassive black holes have tidier feeding habits.
"You wouldn't expect this choking to happen," Pasham noted. "The material around the black hole would be slowly rotating and losing some energy with each circular orbit, but that's not what's happening here."
Scientists hope to study other flares so they can better understand the relationship between supermassive black holes and their host galaxies.
"Almost every massive galaxy contains a supermassive black hole," Pasham said. "But we won't know about them if they're sitting around doing nothing, unless there's an event like a tidal disruption flare."
The research was published earlier this week in Astrophysical Journal Letters.
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