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A supernova is an explosive stellar event whose expanding, heated ejecta can become extraordinarily luminous. Two major physical routes are stellar core collapse in an evolved massive star and thermonuclear disruption of a white dwarf. The observed spectral category and the energy source are distinct: the absence of hydrogen lines alone does not prove a Type Ia supernova.
A light curve follows how deposited energy escapes as the ejecta expand, while spectral lines reveal composition and motion through their Doppler shifts. SN 1987A additionally supplied a neutrino signal that probes the deep collapse rather than only the radiating envelope. Supernovae connect stellar evolution to the production and dispersal of chemical elements, and calibrated Type Ia supernovae provide astronomical distance measurements.