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→Type I
==Type I==
==Type I==
===Type 1a===
Although the exact mechanism that causes type I supernovae is still not entirely understood, for type Ia supernovae, it is generally accepted to occur most often in binary star systems where one of the binary stars is a white dwarf (typically a [[carbon]]-[[oxygen]] dwarf) that is drawing mass from its high mass companion. As the mass from from the companion accumulates on the surface of the [[white dwarf]] it compresses and heats up. Often, the hydrogen in the accumulated mass will heat enough to initiate hydrogen fusion, causing a [[nova]]. If however the white dwarf accumulated enough matter from its companion to have a mass that reaches its [[Chandrasekhar limit]], the white dwarf will no longer be able to support itself via electron degeneracy pressure against the increase in [[gravity]] from the additional mass.<ref>http://adsabs.harvard.edu/abs/1987ApJ...323..140L</ref> A significant portion of the white dwarf will then undergo nuclear fusion within seconds, releasing enough energy to cause the star to explode as a supernova.<ref>http://www.sciencemag.org/cgi/content/abstract/315/5813/825</ref>
Type Ia supernovae are important to [[astronomy]] because they act as standard candles for measuring extra-galactic distances, especially pertaining to other galaxies. This is due to such supernovae explosions having the same luminosity, an absolute magnitude of -19.3 (some five billion times the sun's brightness). The source of this brightness is the generated by radioactive decay of nickel-56. The [[nickel]]-56 is formed during the explosion event itself and decays through [[cobalt]]-56 to [[iron]]-56.<ref>http://adsabs.harvard.edu/abs/2000ARA&A..38..191H</ref>.
In 1998, observations of the apparent magnitude of several type 1a supernovae in other galaxies, resulted in the surprising finding that the universe is expanding at an accelerated rate, due to [[Dark energy|Dark Energy]].<ref>http://arxiv.org/abs/astro-ph/9805201</ref>
===Type 1b and Ic===
Type lb and Ic supernovae, like Type II supernovae, are from massive stars that are running out of core fuel for fusion. However the stars for type Ib explosions had their outer shell of hydrogen lost or striped away, and type Ic are from stars that have lost most of both its [[hydrogen]] and subsequent [[helium]] shell. This loss is either due to intense stellar winds, or from interaction with a nearby binary companion of sufficient mass.<ref>http://adsabs.harvard.edu/abs/1997rdbs.conf..153P</ref> It is believed that type 1b supernovae are from exploding [[Wolf-Rayet]] stars. There is some evidence that a small percentage of type Ic supernovae are the source of [[Gamma-Ray Bursts|Gamma Ray Bursts]].<ref>http://adsabs.harvard.edu/abs/2004MNRAS.349.1093R</ref>
==Type II==
==Type II==