Space scope blinded by faraway blast

An explosion in the depths of the universe was so bright that it briefly blinded a watching satellite, space scientists have revealed. NASA’s orbiting Swift observatory was overwhelmed by the glare of the mysterious eruption, called a gamma-ray burst, despite the fact it happened five billion light-years away.

Blast caught by NASA's Swift telescope
Blast caught by NASA's Swift telescope

That means that the blast – which astronomers think was caused by a star collapsing to form a black hole – occurred before the Sun and planets formed!

Light from the flare-up, labelled GRB 100621A, finally reached Earth on June 21 after travelling nearly halfway across the universe. It battered Swift, which observes the sky with X-ray eyes.

Observing gamma-ray bursts is one of the satellites prime objectives but it was not built to cope with such an intensely bright blast. Dr Phil Evans, of Leicester University’s space department said yesterday: “The burst was so bright when it first erupted that our data-analysis software shut down. So many photons were bombarding the detector each second that it just couldn’t count them quickly enough.

“It was like trying to use a rain gauge and a bucket to measure the flow rate of a tsunami. This burst is one for the record books.”

Dr Evans admits that astronomers did not twig what had happened at first. He returned from a camping holiday in England’s Lake District on June 29 to find that Swift’s software had automatically recorded GRB 100621A’s fade but there was no apparent record of the initial blast. Then he realised it was what had temporarily blinded Swift’s detectors.

Dr Evans and colleagues were able to calculate that the distant explosion had been 140 times brighter than the brightest steady source of X-rays, a neutron star 500,000 times closer to Earth.

Professor David Burrows, of Penn State University, Pennsylvania, who is lead scientist for Swift’s X-ray Telescope (XRT), said: “This gamma-ray burst is by far the brightest light source ever seen in X-ray wavelengths at cosmological distances.”

Neil Gehrels, Swift’s principal investigator at NASA’s Goddard Space Flight Centre, said: “The intensity of these X-rays was unexpected and unprecedented. Just when we were beginning to think that we had seen everything that gamma-ray bursts could throw at us, this burst came along to challenge our assumptions about how powerful their X-ray emissions can be.”

Last year, Swift detected a gamma-ray burst a record 13 billion light-years away, putting it out near the edge of the universe. The previous brightest gamma-ray burst was reported in March 2008.

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By Paul Sutherland

Paul Sutherland has been a professional journalist for nearly 40 years. He writes regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy, plus he has authored three books on astronomy and contributed to others.

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