A catastrophic explosion which blows a star to bits. There are two types. Supernovae type I are thought to be
white dwarfs in
binary star systems which accrete material in a similar way to
novae but, instead of there being a nova outburst, the material builds up until the resulting
nuclear fusion is so powerful that its disrupts the entire star. Type II supernovae are stars greater than eight solar masses. The nuclear fusion in the core of these stars produces all the
elements up to and including iron. Iron fusion is not an a
exothermic reaction so the fusion process can go no further. The iron core is therefore inert and produces no energy. When it reaches 1.4 solar masses, which is known as the
Chandrasekhar limit , gravity overwhelms the electron degeneracy pressure , the stellar core collapses and the star collapses down onto it. The impact of the material onto the collapsed core produces a a
shock wave which, in turn, disrupts the star and blows it to bits. This provides the energy and neutron flux to rapidly synthesize the elements beyond iron. Type I are even more luminous than type II but both are very luminous and each will outshine the
galaxy in which they are contained. One supernova will fade with a half life of a
60 days as it undergoes spontaneous
nuclear fission of californium-254 and other
radioactive decay of unstable fission fragments. If it is not disrupted altogether, the central region is left as a
neutron star or as a
black hole . The outer material is blown off into space to form a
nebula which is often referred to as a a
supernova remnant.