Astronomers using data from NASA’s Chandra X-ray Observatory suggest the giant black hole at the center of the Milky Way may be vaporizing and devouring asteroids, which could explain the frequent flares observed.
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For several years Chandra has detected X-ray flares about once a day from the supermassive black hole known as Sagittarius A*, for short Sgr A*. The flares last a few hours with brightness ranging from a few times to nearly one hundred times that of the black hole’s regular output. The flares also have been seen in infrared data from ESO’s Very Large Telescope in Chile. A new study provides a possible explanation for the mysterious flares. The suggestion is that there is a cloud around Sgr A* containing hundreds of trillions of asteroids and comets, which have been stripped from their parent stars. Asteroids passing within about 100 million miles of the black hole, roughly the distance between the Earth and the sun, would be torn into pieces by the tidal forces from the black hole. These fragments then would be vaporized by friction as they pass through the hot, thin gas flowing onto Sgr A*, similar to a meteor heating up and glowing as it falls through Earth’s atmosphere. A flare is produced and the remains of the asteroid are swallowed eventually by the black hole. The authors estimate that it would take asteroids larger than about six miles in radius to generate the flares observed by Chandra. Meanwhile, Sgr A* also may be consuming smaller asteroids, but these would be difficult to spot because the flares they generate would be fainter. Planets thrown into orbits too close to Sgr A* also should be disrupted by tidal forces, although this would happen much less frequently than the disruption of asteroids, because planets are not as common. Very long observations of Sgr A* will be made with Chandra later in 2012 that will give valuable new information about the frequency and brightness of flares and should help to test the model proposed here to explain them.