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A black hole has been spotted belching out a burst of gamma rays after gulping down part of a nearby star, something never seen before. Such violent burps may actually be the most common type of explosive 鈥済amma-ray burst鈥� in the universe.

The event was named GRB 070610 after the date of its discovery by NASA鈥檚 Swift satellite on 10 June 2007.

At first it looked like another ordinary long gamma-ray burst (GRB) in a distant galaxy. These outbursts are thought to be the death cries of massive stars collapsing to form black holes.

But this GRB seems to have a different provenance altogether. Astronomers led by Mansi Kasliwal of Caltech in Pasadena, US, traced the burst to a star system in our own galaxy, where a black hole and a star are orbiting each other.

They suspect that the black hole in the system had some kind of a giant hiccup while chowing down on matter stolen from its companion star. Watch an animation of a .

This gamma-ray hiccup behaviour has never been seen before and scientists are not sure how to explain it. But though the burst was much less powerful than typical long GRBs, such events are still quite violent. A similar system called V4641 Sgr set the record for spewing matter out at the highest speed ever observed in our galaxy during a similar outburst, observed in X-rays, in 1999.

Close range

Observing this black hole outburst from nearby would be a risky prospect. 鈥淚f you were as close to the black hole as the [companion] star, things wouldn鈥檛 be pretty,鈥� Kasliwal told 51动漫. 鈥淚 don鈥檛 think you鈥檇 want to be near it.鈥�

But there is no need to be concerned about gamma-ray outbursts from pairings of black holes and stars in our galaxy, Kasliwal adds. 鈥淭he closest ones we know of are [still] far enough that we probably don鈥檛 need to worry about it,鈥� she says.

Krzysztof Stanek of Ohio State University in Columbus, Ohio, US, who is not a member of Kasliwal鈥檚 team, says this new type of event could be an exciting new phenomenon to study, if more can be found. 鈥淚t鈥檚 clearly an unusual event. There鈥檚 yet another way that nature found to make GRBs, which is very interesting,鈥� he told 51动漫.

Kasliwal says this kind of event is probably much more common than the ones normally observed by Swift.

Low energy

鈥淭he reason we haven鈥檛 seen something like this before is not because it鈥檚 rare but because it鈥檚 a low-energy event,鈥� Kasliwal says, explaining that this burst is intrinsically about 100 trillion times less powerful than previously observed long GRBs. 鈥淚f the same thing happened in another galaxy, we just don鈥檛 have detectors that are sensitive enough to see it.鈥�

Those more powerful long GRBs have only been observed in other galaxies and are thought to occur in our own galaxy less than once every 100,000 years. By contrast, Kasliwal says events like the one her team observed may occur once per decade in the Milky Way.

Indeed, only a few GRBs have ever been seen in our galaxy, but these have been of the 鈥榮hort鈥� variety, which typically last less than one second. One such short GRB 鈥� caused by a starquake on a dense stellar corpse called a neutron star 鈥� was observed in the Milky Way in December 2004 (see Starquake explosion rips neutron star open ).