Astronomers have observed possibly the biggest blast ever seen in the cosmos. When NASA's SWIFT space observatory first spotted it 10 days ago, observers thought it was a massive star blowing up as a supernova and expected it to fade within hours or even minutes. But the high-energy radiation from the source has shown no sign of dying down, which suggests that astronomers may have caught a star in the process of being ripped to shreds by a black hole.
The blast is actually a series of bursts, like a string of firecrackers going off one after another. "We know of objects in our own galaxy that can produce repeated bursts, but they are thousands to millions of times less powerful than the bursts we are seeing," says Andrew Fruchter of the Space Telescope Science Institute in Baltimore, Maryland. "This is truly extraordinary."
SWIFT's Burst Alert Telescope detected the source of the bursts on 28 March. The Hubble Space Telescope took an image of the source on 4 April, which located the explosions at the center of a galaxy 3.8 billion light-years away. On the same day, NASA's Chandra X-ray Observatory took a picture of the source by pointing at it for 4 hours. That image also showed that the source of the bursts was at the center of the galaxy imaged by Hubble.
The position of the source within the galaxy offered a clue that the bursts might be associated with a black hole, as nearly all galaxies have a black hole in the middle. "We think that there is a dormant black hole there that has accreted a lump of matter—probably a star that has fallen into it," says astrophysicist Neil Gehrels, the lead scientist for SWIFT at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
What could be going on is the following: A star flitting too close to the black hole has been grabbed by its gravitational pull. The star's gas has been falling into the black hole, causing enormous amounts of energy to be released in the form of high-energy particles shooting out like a jet.
Although this is not the first time astronomers have witnessed a star being gobbled up by a black hole, the bursts are putting out energy far greater than previously seen. One reason for the extreme brightness could be that the jet of particles shooting out of the black hole is pointing straight at Earth.
Astronomers all over the world are working round the clock to collect more data on the event, and Hubble is snapping more images of the source. "Some spectra have been taken; there's a lot more work to be done on how the spectrum changes over time," Gehrels says. "If it really is a star being torn up, then we'd expect it to fade away in the next few days. If it stays bright for several weeks or a month, that would tell us something different. I'm not sure what that would be."