Supernova 1987a

On the night of February 23-24, 1987, a star in the Large Magellanic Cloud, a satellite galaxy of the Milky Way, underwent a supernova explosion. The progenitor star is identified as being an 18 solar mass B3 supergiant that, having exhausted its nuclear fuel, imploded its core and ejected its outer layers. Because this event was the nearest supernova visible in modern times, it was studied in great detail by a myriad of instruments covering the whole range of the electromagnetic spectrum.

Standard models of the supernova event predict that neutrinos are emitted in a burst at the moment of core collapse when electron-positron pairs, produced by the high energy gamma rays present at such enormous temperatures and densities, are themselves annihilated. Because the neutrinos are emitted at the very first instant of the supernova event, the neutrino burst should precede the detection of the increase in optical luminosity, which itself takes place when the resultant shock wave travels outward through the star from the core, at a velocity less than the speed of light. The burst of neutrinos from SN1987a was indeed evident in data obtained both with the Kamiokande II detector in Kamioke, Japan and the IMB detector located near Cleveland, Ohio. SN1987a thus became the second detected source of cosmic neutrinos, the first being the Sun.

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