Animation of the formation of a type Ia supernova. This is the explosive end of a white dwarf star in a binary star system, in which the dwarf is accretes matter from its larger companion. The dwarf is the dead core of an old star, formed mainly of carbon and oxygen, which its parent did not have sufficient mass to burn. However, the infalling matter from the companion star can raise the pressure, density and temperature of the dwarf so much that it does ignite carbon fusion. This fusion rapidly spreads through the dwarf, providing enough energy to completely unbind the star's material in a huge explosion. The critical mass and temperature required to ignite carbon fusion is the same for all white dwarf stars, so all type Ia supernovae are the same brightness and exhibit very similar spectral features, which makes them useful \standard candles\ for measuring distances in space.