Supernova

A supernova is a powerful stellar explosion that marks the end of a star's life and briefly outshines entire galaxies. It releases about 10^44 joules (roughly 10^51 ergs) of energy over weeks to months and disperses heavy elements into the interstellar medium. They are observed in all types of galaxies and have important roles in chemical enrichment and star formation.

The main classes are Type I and Type II. Type II result from the core collapse of massive stars and show hydrogen lines in their spectra. Type I lack hydrogen and include Type Ia, Ib, and Ic. Type Ia arise from thermonuclear disruption of a white dwarf in a binary that accretes matter to near the Chandrasekhar limit, identifiable by a silicon absorption line near 615 nm and lack of hydrogen. Type Ib and Ic are core-collapse events from massive stars that have lost most of their outer envelopes; Ib shows helium lines, Ic does not.

Progenitors and mechanism: Type II, Ib, and Ic originate from stars more than about 8 solar masses. Core collapse leaves a neutron star or black hole; the explosion is driven by the collapse dynamics and neutrino heating. Type Ia originate in binary systems where the white dwarf approaches the Chandrasekhar mass and undergoes runaway carbon fusion; the detonation unbinds the star.

Outcomes and importance: Supernovae seed the interstellar medium with heavy elements and can trigger star formation. They produce remnants such as the Crab Nebula from SN 1054 and SN 1987A in the Large Magellanic Cloud. Type Ia supernovae serve as standardizable candles for measuring cosmic distances, contributing to the discovery of dark energy.