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Cosmic flashbulb effect caused by 'black-hole invaders'

Whirly star-gobble intrusions to blame, seemingly

Boffins at Leeds Uni say they have come up with a new explanation for the mysterious astronomical phenomena known as "gamma ray bursts" (GRBs) because they consist of bursts of gamma rays.

GRBs, originally noted by US military spy sats looking for evidence of surreptitious commie nuke tests, are puzzling because of their incredible power. According to NASA, the typical GRB flares "about a million trillion times as brightly as the Sun", lasting anywhere from a few milliseconds to a couple of hours.

The mysterious cosmic flashbulbs pop off about once a day from random directions in the sky, and boffins have struggled to work out what causes them ever since they were detected in the 1960s.

Of late, a leading theory has suggested that GRBs are caused following the explosive supernova demise of giant stars, which then collapse to form a central black hole girdled by a disc of matter. This disc then tends to belch axial jets of unfeasibly incandescent plasma heated by neutrino emissions. The incandescence of the jets is the source of the gamma rays in GRBs.

Now, however, some boffins have disparaged this theory, saying that neutrino heating can't possibly be sustained long enough to produce the lengthiest GRBs observed by the Swift satellite. They say it's likelier that rather the gamma zap mechanism involves the collapsing star spinning violently about the central black hole, so prolonging the destruction process as centripetal forces war with the hole's pull.

Leeds-based boffins have now come up with a new wrinkle on this model, in which a smallish passing black hole actually falls into a star. As it plunges toward the centre, the while consuming its host, it also sets the doomed star spinning furiously - so slowing the final cataclysm down enough to produce a longer GRB. Leeds Uni spokespersons describe such black holes as "invaders".

"The results correlate very well with observations from satellites,” says Professor Serguei Kommissarov of the Leeds mathematics department.

Proper hard-sums explanation is available here, and soon apparently in prestigious astroboffinry mag Monthly Notices of the Royal Astronomical Society. ®

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