Wikipedia:Today's featured article/June 18, 2011

Gamma-ray bursts (GRBs) are flashes of gamma rays associated with extremely energetic explosions in distant galaxies. GRBs are the most luminous electromagnetic events known to occur in the universe. A burst typically lasts 20–40 seconds, but can last from ten milliseconds to several minutes. The initial burst is usually followed by a longer-lived "afterglow" emitted at longer wavelengths. Most observed GRBs are believed to be a narrow beam of intense radiation released during a supernova event, as a rapidly rotating, high-mass star collapses to form a neutron star or black hole. The sources of most GRBs are billions of light years from Earth, implying that the explosions are both extremely energetic and extremely rare. GRBs were first detected in 1967 by the Vela satellites, but it was not until 1997 that they were better understood, with the detection of the first X-ray and optical afterglows and the use of optical spectroscopy to directly measure their redshifts. (more...)

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