- The catastrophic and explosive disruption of a heavy star late in its evolution. Some supernovae are bright enough to outshine the galaxy in which they erupt. Supernovae are now known to be major sources of material erupted into interstellar space. They are the origin of all the universe’s heavy elements – those beyond iron in atomic weight – as well as producing intense cosmic rays and severe shock waves. They can only arise from stars of more than some 9 solar masses, and result from shock waves sent out as the core of such a star collapses. There is also a second category of supernova explosion, less well known than this classic type, apparently affecting smaller stars with white dwarf companions. A galaxy as large as ours has a supernova every few decades, although it may be impossible to observe if it is hidden by the centre of the galaxy.