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Last Updated: Wednesday, 16 April, 2003, 09:06 GMT 10:06 UK
Gamma-ray burst mystery solved
By Dr David Whitehouse
BBC News Online science editor

Gamma Ray Burster
Now you see it. The recent burst.

Scientists may have solved one of astronomy's major puzzles: the origin of powerful gamma-ray bursts.

For a few seconds, these bursts can pour out more radiation than anything else in the cosmos.

About once a day, a flash of high-energy radiation coming from deep space and lasting only a few seconds is detected by satellite observatories orbiting the Earth. The enormous power of the energy bursts has long mystified astronomers.

Now, thanks to a burster that was remarkably close in cosmic terms, their true nature may have been revealed. The bursts seem to come from exploding stars called supernovae.

"There should no longer be doubt in anybody's mind that gamma-ray bursts and supernovae are connected," says Thomas Matheson, of the Harvard-Smithsonian Centre for Astrophysics, US, a member of the team that made the discovery.

Outshining the Universe

In the late 1960s, US military satellites designed to look for clandestine nuclear tests picked up powerful bursts of radiation coming from deep space.

Before the burst
...and now you don't. Before the burst happened

They appeared to come from far beyond our galaxy, from distances comparable with the overall size of the Universe.

But coming from such large distances meant that the energy in the burst was incredible and astronomers struggled to explain them.

Various theories were proposed including collisions between black holes or neutron stars that would have liberated vast amounts of energy. But no explanation was completely satisfactory.

As technology improved, astronomers were able to react more swiftly to these fleeting events and turn their telescopes towards them while they lasted, where they sometimes detected a fading optical glow from the same strange object.

The latest breakthrough began on 29 March when the High-Energy Transient Explorer satellite (Hete) detected one of the brightest and closest gamma-ray bursts ever seen.

Located in the constellation of Leo, the 30-second burst, designated GRB 030329, outshone the entire Universe in gamma rays. Its optical afterglow was still over a trillion times brighter than the Sun over two hours later.

Caught in the act

After news of the latest burst was relayed around the world, astronomers working at the 6.5-metre Multiple Mirror Telescope (MMT) at Mount Hopkins in Arizona, US, were able to interrupt their schedule to look at the burster.

The Multiple Mirror Telescope
The Multiple Mirror Telescope

"We caught it in the act," says Matheson. "The burst was approximately two billion light-years from Earth, as opposed to other bursts located upwards of 10 billion light-years away.

"For the first time, we were measuring an event no other human beings had seen before," adds Krzysztof Stanek of Harvard, US. "The MMT was our magic time machine that we used to capture this catastrophic cosmic event."

The astronomers detected direct evidence that the afterglow of the burst exhibits the same patterns as light from a supernova.

A supernova is the explosion of a star at least eight times as massive as the Sun. When such stars deplete their nuclear fuel, they no longer have the energy to support their mass.

Consequently, their cores implode, forming either a neutron star or (if there is enough mass) a black hole. The stars' outer atmospheres are blown off into space.

At the moment, researchers cannot yet determine the timing of the gamma burst relative to the supernova (whether one preceded the other or whether both began at the same time), but the same event - a star explosion - was certainly the trigger for both, they say.

"All gamma-ray bursts may have associated supernovae that are too faint to observe," says Matheson, who believes that because the burst was both close and bright, the supernova was detectable.

"It was detailed observations of the afterglow on subsequent nights that provided the vital clues. In the fading light, astronomers spotted the telltale signs. The mystery may be solved," he says.

Scattered spacecraft pinpoint cosmic burst
18 Oct 00  |  Science/Nature
Space blast teaser
25 Mar 99  |  Science/Nature

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