Post by Joanna on Apr 1, 2017 23:22:10 GMT -5
Mysterious Flash from a Galaxy Far, Far Away
It was a spark in the night. A flash of x-rays from a galaxy hovering nearly invisibly on the edge of infinity. Astronomers say they do not know what caused it.
The orbiting Chandra X-ray Observatory was in the midst of a 75-day survey of a patch of sky known as the Chandra Deep Field-South, when it recorded the burst from a formerly quiescent spot in the cosmos. For a few brief hours on Oct 1, 2014, the x-rays were a thousand times brighter than all the light from its home galaxy, a dwarf unremarkable speck almost 11 billion light years from Earth in the constellation Fornax. Then whatever had gone bump in the night was over and the x-rays died.
The event as observed does not fit any known phenomena, according to Franz Bauer, an astronomer at Pontifical Catholic University of Chile, and lead author of a report to be published in Science. The most likely explanation, he said in the paper and during an interview, is that the x-rays are the afterglow from a gamma ray burst seen sideways, caused by the collapse of a massive star into a black hole, or the collision of a pair of the dense stellar remnants called neutron stars, that squirt gamma rays in one direction only. If Earth is out of the beam, then all astronomers will see is an “orphan afterglow.” But if this were the case, a typical afterglow would appear about a hundred times more intense than it is, Bauer added, unless this was an unusually weak event, or it came from much farther away – from something far behind the little galaxy.
Another possibility, astronomers contend, is that this was the result of a star being torn apart by a black hole, but that would produce a different spectrum of x-rays. In other words, none of the usual cosmic catastrophe suspects works. “Unfortunately there is no ‘smoking gun’ evidence that favors one scenario over the other here,” Bauer admitted. Astronomers’ best chance of understanding this “transient,” as he called it, is to find more examples.
Chalk up another mystery to nature’s repertoire. Or could it have been something even more “out of this world”?
Source: Dennis Overbye, The New York Times, March 31, 2017.