A place far, far away: This image merges data from Swift's Ultraviolet/Optical (blue, green) and X-Ray (orange, red) telescopes. No visible light accompanied the burst, which hints at great distance.

Credit: NASA/Swift/Stefan Immler

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SYDNEY: Astronomers have recorded the light of a gamma-ray burst, which they believe comes from the oldest, and most distant object ever observed in the universe.

At 13 billion light-years away, the burst occurred when the universe was just five per cent of its current age, or 630 million years old. This provides the first evidence that the young universe, only a few hundred million years after the Big Bang, was already home to exploding stars and black holes.

Record-breaker

"This new gamma-ray burst smashed all the records," said Edo Berger, part of the team at the Harvard-Smithsonian Centre for Astrophysics in Boston, Massachusetts, who made the discovery. "It easily surpassed the most distant galaxies and quasars. In fact, it showed that we can use these spectacular events to pinpoint the first generation of stars and galaxies."

Gamma-ray bursts occur when massive stars exhaust their nuclear fuel. The core of the star collapses, and jets of gas are expelled, blasting into other gases released by the star, generating heat and light. See an animation of a massive gamma-ray burst here.

When light from such an explosion was emitted in an event very far away, the expansion of the universe subsequently causes the spectrum to shift (the 'red shift'), with visible light stretching into longer, infrared wavelengths.

Similarly, ultraviolet light shifts into the visible spectrum. This light is absorbed, however, by hydrogen gases in the early universe. Hence, when a scientist's telescope captures infrared light, but no visible light, they may be looking at an ancient gamma-ray burst.

Red shifted

In the early hours of 23 April 2009, the Swift satellite tuned its telescopes onto just such a burst. A fading X-ray afterglow, but no visible light, was observed by Berger's team.

Shortly afterwards, a second telescope located on Mauna Key, Hawaii, confirmed the presence of infrared light in the afterglow. Spectral measurements placed the burst's red shift at '8.2' – 190 million light years further away than the last record holder, which had a red shift of only 6.7.

"Swift was designed to catch these very distant bursts," said Swift lead scientist Neil Gehrels at NASA's Goddard Space Flight Centre in Greenbelt, Maryland. "The incredible distance to this burst exceeded our greatest expectations – it was a true blast from the past."

John Dickey, an astronomer from the University of Tasmania, commented that these are exciting, if circumstantial, observations. "It would be very interesting to confirm the red shift by following up with a detection, and a spectrum, of the host galaxy," he said, but cautioned that such measurements may still be 20 years away.