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Gamma-Ray Bursts

Astronomers are only just determining the mystery of what exactly gamma-ray bursts (GRBs) are.
The latest theory is thus: A gamma-ray burst is a bright burst of gamma-rays typically milliseconds to tens of seconds long. Sometimes telescopes see a bright optical "afterglow" hours later. Astronomers suspect the gamma-rays come from narrow jet-like structures in exploding stars. Detectors first saw GRBs in the 1960s.
The more popular theory determining what GRBs are, is that gamma-ray bursts are produced when the most massive stars in the Universe explode in a supernova, and the majority of the most massive stars existed early in the Universe, which corresponds to a large distance from us.
NASA's Swift telescope recorded a gamma-ray burst on 18th February 2006. Then several other powerful telescopes followed the explosion.
Astronomers know that GRBs are somehow connected with supernovae (see "Supernovae" topic page) but are not entirely sure what the connexion is, as not all supernovae explosions come along with a GRB.
The February burst took place in a galaxy 440 million lightyears away, in the constellation Aries. An X-ray flash more than likely erupted from a high-energy jet piercing out from the core of a star on the verge of exploding. The GRB lasted almost 40 minutes. The burst faded away after a few minutes as the star blew itself to pieces, creating a shock wave.
Astronomers believe that this was the beginning of a supernova, because they don't usually detect supernovae until a few days after the initial explosion when they become optically bright.
Two days later, the explosion did in fact look like a "classical" supernova, with a glowing gas cloud and debris starting to outshine the shock wave.
Fully-fledged GRBs may tap the huge gravitational energy of black holes, which form only when the most massive stars explode.


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