The spectacular blast, which occurred in September in the Carina constellation, produced energies ranging from 3,000 to more than five billion times that of visible light, astrophysicists said.

"Visible light has an energy range of between two and three electron volts and these were in the millions to billions of electron volts," astrophysicist Frank Reddy of US space agency NASA told AFP.

"If you think about it in terms of energy, X-rays are more energetic because they penetrate matter. These things don't stop for anything -- they just bore through and that's why we can see them from enormous distances," Reddy said.

A team led by Jochen Greiner of Germany's Max Planck Institute for Extraterrestrial Physics determined that the huge gamma-ray burst occurred 12.2 billion light years away.

The sun is eight light minutes from Earth, and Pluto is 12 light hours away.

Taking into account the huge distance from earth of the burst, scientists worked out that the blast was stronger than 9,000 supernovae -- powerful explosions that occur at the end of a star's lifetime -- and that the gas jets emitting the initial gamma rays moved at nearly the speed of light.

"Gamma-ray bursts as a class qualify as the biggest explosions since the Big Bang and in the measurements we reported, this is the most intense and the most extreme," Reddy said.

Astronomers believe gamma-ray bursts occur when stars run out of nuclear fuel and collapse.

They shine hundreds of times brighter than a typical supernova and about a million-trillion times as bright as earth's sun, NASA says on its website.

Long gamma-ray bursts, which last more than two seconds, occur in massive stars that are undergoing collapse, while short bursts lasting less than two seconds occur in smaller stars.

In short gamma-ray bursts, stars simply explode and form supernovae, but in long bursts, the enormous bulk of the star leads its core to collapse and form a blackhole, into which the rest of the star falls.

As the star's core collapses into the black hole, jets of material blast outward, boring through the collapsing star and continuing into space where they interact with gas previously shed by the star, generating bright afterglows that fade with time.

By studying gamma-ray bursts -- called GRBs -- scientists are trying to gain a better understanding of the origins of the early universe, "the parts we can't fully see yet," Reddy told AFP.

"Remember: these are single stars that we're able to see at distances where we can't even reliably see galaxies. This is our only signal from that far away," he said.

Last month, NASA announced that it had detected molecular lines in a GRB spectrum.

"That's the chemical signature of a galaxy that's extremely far away," said Reddy.

"That's the promise that the study of GRBs has held out for a long time and only now is bearing fruit: that you will be able to get these samples of extremely far cosmos. One day, we will see GRBs from some of the earliest stars," he said.

The Fermi telescope and NASA's Swift satellite detect "in the order of 1,000 gamma-ray bursts a year, or a burst every 100,000 years in a given galaxy," said Reddy.

Astrophysicists estimate there are hundreds of billions of galaxies.

The Fermi gamma-ray space telescope was developed by NASA in collaboration with the US Department of Energy and partners including academic institutions in France, Germany, Italy, Japan, Sweden and the United States.

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