Supernova explosion. Artwork of a star ending its life in a supernova explosion (upper left). A companion star to the one undergoing the supernova is seen at lower right, being flung from the system by the explosion. Supernovae occur at the end of the life of a massive star. When it has used up all its nuclear fuel, it is unable to support itself against gravity. The outer layers then collapse inwards, compressing the core until it is so dense that it cannot be compressed any more. The collapsing outer layers then rebound from it in a huge explosion.