Giant Black Hole Shreds and Swallows Helpless Star

Ken Croswell in Science:

ScreenHunter_25 May. 10 11.11Some people seem born under an unlucky star. But some stars are equally unlucky themselves. Astronomers have spotted a star in another galaxy plunging toward a giant black hole and being ripped to shreds, sparking a flare so brilliant that observers detected it from a distance of 2.1 billion light-years. By watching the flare brighten and fade, scientists have achieved the unprecedented feat of reconstructing the life story of the doomed sun.

Giant black holes occupy the centers of most large galaxies, including our own, whose central black hole is 4 million times as massive as the sun and swallows a star once every 10,000 to 100,000 years. Astronomers have recently seen black holes in several other galaxies rip stars apart. But the new drama is unique. “This is the first time where we're really seeing one of these events from start to finish,” says astronomer Suvi Gezari of Johns Hopkins University in Baltimore, Maryland. “What was so spectacular was the fact that we actually could figure out what type of star was disrupted.”

Astronomers first picked up a signal from the constellation Draco in May 2010, when the Pan-STARRS 1 telescope in Hawaii spotted a flare at visible and near-infrared wavelengths. The scientists calculate that the black hole's gravity had torn the star apart a month earlier by pulling harder on one side of the star than the other. As stellar debris funneled into the black hole, gravity and friction roasted the star's remains until they emitted ultraviolet radiation, which NASA's GALEX satellite detected in June. The flare peaked in July 2010, outshining all the stars in the galaxy put together, and then faded, but was still aglow a year later.

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