What is a Supernova? There are two types of supernovae: Type 1 modeled to be a binary star system in which one star becomes a white dwarf, and begins accreting mass from its companion until it is able to collapse. about 1.4 solar masses is required. These only occur in elliptical galaxies. Type 2 only occur in massive stars. Near the end of its life some of a star's mass flows towards its core, and it differs on how massive they are, but end in the same result. For helium cores from 2.2 and 2.5 solar masses (helium cores are about 1/4 of the original mass) a neon-oxygen core forms post carbon burning. When the core reaches a density of about 2.5 x 10^10 g/cm^3 the oxygen ignites. For 2.5 to 2.8 solar mass helium cores an iron core collapse is caused by a combination of photodisintegration and electron capture. These only occur in the arms of spiral galaxies. Image taken from http://hyperphysics.phy-astr.gsu.edu