Friday, December 18, 2015
Astronomers Watch Black Hole Burp After Eating a Star
Scientists have for the first time witnessed a black hole swallow a star and then quickly eject a flare of stellar debris moving at nearly light speed.
Astrophysicists tracked the star—about the size of our sun—as it shifted from its customary path, slipped into the gravitational pull of a supermassive black hole, and was sucked in, says Sjoert van Velzen, a Hubble fellow at Johns Hopkins University.
“These events are extremely rare,” says van Velzen, lead author of the study published in the journal Science. “It’s the first time we see everything from the stellar destruction followed by the launch of a conical outflow, also called a jet, and we watched it unfold over several months.”
Black holes are areas of space so dense that irresistible gravitational force stops the escape of matter, gas, and even light, rendering them invisible and creating the effect of a void in the fabric of space.
Astrophysicists had predicted that when a black hole is force-fed a large amount of gas, in this case destroying a whole star, then a fast-moving jet of wreckage in the form of plasma—elementary particles in a magnetic field—can escape from near the black hole rim, or “event horizon.” This study suggests this prediction was correct, the scientists say.
“Previous efforts to find evidence for these jets, including my own, were late to the game,” adds van Velzen, who led the analysis and coordinated the efforts of 13 other scientists in the United States, the Netherlands, Great Britain, and Australia.
Supermassive black holes, the largest of black holes, are believed to exist at the center of most massive galaxies. This particular one lies at the lighter end of the supermassive black hole spectrum, at only about a million times the mass of our sun, but still packing the force to gobble a star.
It all started with a tweet
The first observation of the star on its path to destruction was made by a team at the Ohio State University, using an optical telescope in Hawaii. That team announced its discovery on Twitter in early December 2014.
After reading about the event, van Velzen contacted an astrophysics team led by Rob Fender at the University of Oxford in Great Britain. That group used radio telescopes to follow up as fast as possible. They were just in time to catch the action.
By the time it was done, the international team had data from satellites and ground-based telescopes that gathered X-ray, radio and optical signals, providing a “multi-wavelength” portrait of this event.
It helped that the galaxy in question is closer to Earth than those studied previously in hopes of tracking a jet emerging after the destruction of a star. This galaxy is about 300 million light years away, while the others were at least three times farther away. One light year is 5.88 trillion miles.
The first step for the international team was to rule out the possibility that the light was from a pre-existing expansive swirling mass called an “accretion disk” that forms when a black hole is sucking in matter from space. That helped to confirm that the sudden increase of light from the galaxy was due to a newly trapped star.
“The destruction of a star by a black hole is beautifully complicated, and far from understood,” van Velzen says. “From our observations, we learn the streams of stellar debris can organize and make a jet rather quickly, which is valuable input for constructing a complete theory of these events.”
Support for this study came from multiple sources, including NASA, the Netherlands Foundation for Scientific Research (NOW), the European Research Council, the International Centre for Radio Astronomy Research, the Alfred P. Sloan Foundation, and the Australian Research Council.