One of the last remnants of a dead galaxy — a medium-sized black hole — may be devouring a companion star, taking a bite when the star comes close every year or so. As the black hole swallows the stolen gas, it flares brightly, producing an outburst of X-rays that slowly fades — until the next bite.
The object is known as ESO 243-49 HLX-1. It orbits a large spiral galaxy that’s almost 300 million light-years away.
HLX-1 was discovered in observations by an X-ray telescope in space. The X-rays suggested the object was a disk of superhot gas around a black hole. Follow-up observations allowed astronomers to measure the mass of the central black hole: about 20,000 times the mass of the Sun — one of only a handful of possible black holes of that size discovered so far.
HLX-1 brightens and fades roughly once a year. A possible explanation is that the disk of gas is fed by a star in a stretched-out orbit. When the star comes close, the black hole pulls gas from its surface. The gas funnels into the disk, creating a burst of X-rays. The black hole then swallows some of the gas, so the disk fades.
The black hole may be surrounded by a cluster of stars. That could mean that the whole group was originally the core of a small galaxy. The large galaxy it orbits today stripped away its outer regions — leaving a hungry black hole that’s slowly eating one of the galaxy’s few remaining stars.
Script by Damond Benningfield, Copyright 2012