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Gamma-ray burst
flashes of gamma rays from distant galaxies / From Wikipedia, the free encyclopedia
Gamma-ray bursts (GRBs) are flashes of gamma rays from extremely energetic explosions. They have been seen in distant galaxies. They are the most luminous electromagnetic events known to occur in the universe.
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Bursts can last from milliseconds to several minutes, although a typical burst lasts a few seconds. The initial burst is usually followed by a longer-lived 'afterglow' emitted at longer wavelengths (X-ray, ultraviolet, visible light, infrared and radio waves).
Most GRBs are a narrow beam of intense radiation released during a supernova, as a huge rapidly spinning star collapses to form a black hole. A subclass of GRBs (the 'short' bursts) seem to come from a different process, perhaps the merger of binary neutron stars.
The sources of most GRBs are billions of light years away from Earth. This suggests the explosions are extremely energetic: a typical burst releases as much energy in a few seconds as the Sun will in its entire 10 billion year lifetime.[1] They are very rare (a few per galaxy per million years).[2]
All observed GRBs have come from outside the Milky Way galaxy. Similar phenomena, soft gamma repeater flares, are associated with magnetars within the Milky Way. It has been suggested that a gamma-ray burst in the Milky Way could cause a mass extinction on Earth.[3] No such case is known.