Share Astronomers think they've nailed down the source of a mysterious blast of gamma rays that reached Earth in late March and continues, at reduced levels, even today. The culprit looks like a black hole, 3.8 billion light-years away, that swallowed and ripped apart a wandering star.

On March 28, NASA's Swift satellite first noted the outburst of invisible radiation, a gamma ray burst, one of the most powerful explosions in the universe. Such blasts, thought to result from the explosion of massive stars, are regularly detected and usually die away within minutes.
But this one continues today, and in its first two days, the intensity of the outburst measured in some wavelengths not visible to the naked eye as bright as a hundred billion suns, scientists report in Thursday's edition of the journal Science. That makes it one of the most intense cosmic explosions ever witnessed by astronomers.
“This is probably the first time mankind has seen a phenomenon like this,” says astronomer Josh Bloom of the University of California -- Berkeley, lead author of one of two studies on the outburst. The finding adds to evidence that most galaxies, including our own Milky Way, likely harbor titanic black holes at their center, mostly quiet, but always waiting to pull part anything that wanders too close.
“It has been a long detective story, figuring this out,” he says. Swift and other satellites narrowed the origin of the March blast to the center of a galaxy about 22.4 billion trillion miles away. Most gamma ray bursts originate instead from the edges of galaxies, the islands of stars filling space, and are thought to result from the sudden collapse of large stars.
“Most galaxies, including ours, have a super-massive black hole in their center ,” Bloom says. An analysis presented by his team and another led by Andrew Levan of the United Kingdom's University of Warwick suggest the mystery outburst resulted when a black hole, one weighing as much as 10 million times more than the sun, ripped apart a wandering star, nearly instantaneously, and then feasted off its gases.
Intense heating of those gases, pulled into a ring circling the distant black hole at nearly the speed of light, led to beams of radiation shooting off from the black hole. One of those beams was pointed directly at Earth, which has an atmosphere that shields it from the blast's effects, but where it was detected by the Swift satellite. The blast had taken 3.8 billion years to reach Earth.
“Seeing a star get ripped apart by a black hole from almost 4 billion light-years away, that's a remarkable thing,” says astronomer Dave Goldberg, co-author of A User's Guide to the Universe: Surviving the Perils of Black Holes, Time Paradoxes, and Quantum Uncertainty, who was not part of the studies. “We want to study black holes because they are tremendous natural laboratories for what happens to matter at very high energies.”
Only about 10% of all galaxies appear to have super-massive black holes actively feasting on stars and gas, Bloom says. Most, including the one at the center of our Milky Way galaxy, appear dormant. “It is only a lucky accident of geometry that this one blast was pointed in just our direction,” he adds.
On Wednesday, NASA's Chandra X-ray telescope team reported evidence that even the earliest galaxies, ones born within 1 billion years of the Big Bang about 13.7 billion years ago, harbored “baby” versions of such black holes.
Rather than devouring the first galaxies, they appear to have helped each other grow in tandem, said astrophysicist Ezequiel Treister of the University of Hawaii at Manoa, at a NASA briefing.
“Clearly, we now know that black holes play a big role in the construction of galaxies, and the origin of stars like our own,” Goldberg says. “Ultimately, we are made of star stuff, so understanding black holes helps us understand ourselves.”
(Source: USA TODAY