Remnant of Supernova 1987A. Photographed by the Hubble Space Telescope, Wide Field Planetary Camera 2. Supernovae are massive stellar explosions which throw the outer layers of a star off into space. The quantity of energy released by a supernova can be equivalent to the energy output of the Sun over its entire lifetime. They briefly become what appears to observers as a bright new star, hence the name. Supernova 1987A was first observed within hours of exploding and offered astronomers their first opportunity to test theories of supernova formation against observational evidence. It occurred in the Large Magellanic Cloud, a dwarf galaxy outside the Milky Way, and was caused by the explosion of a blue supergiant star some 20 times the mass of the Sun.
