Supernovae

A supernova is a powerful stellar explosion that marks the end of certain stars' life cycles. They briefly outshine entire galaxies and release as much energy in a few weeks as the Sun would over its entire lifetime. Supernovae are observable across cosmic distances, serving as transient astronomical events that illuminate the processes of stellar evolution, nucleosynthesis, and galactic dynamics.

There are two broad families: core-collapse supernovae (types II, Ib, Ic) and thermonuclear supernovae (type Ia). Core-collapse arise when massive stars (roughly more than 8 solar masses) exhaust nuclear fuel and their cores collapse under gravity, forming a neutron star or black hole. The outer layers are expelled in a powerful explosion. Spectra of type II display hydrogen lines; type Ib lack hydrogen but show helium; type Ic lack both hydrogen and helium. Type Ia originate in binary systems where a white dwarf accretes material from a companion; reaching a critical mass near the Chandrasekhar limit triggers a thermonuclear runaway that disrupts the star. Type Ia spectra lack hydrogen and helium features but show strong silicon absorption near peak brightness.

Observationally, supernovae produce characteristic light curves and spectra that evolve over days to months. They enrich the interstellar medium with heavy elements such as iron and nickel. They often leave behind compact remnants, including neutron stars or black holes. Supernovae occur in all galaxy types, with roughly a few per millennium in a galaxy like the Milky Way, and are used to measure extragalactic distances and study cosmic expansion.