Type II supernova

A stellar explosion classified by hydrogen lines in its spectrum, usually produced when a massive star’s iron core collapses while a hydrogen-rich envelope remains.

Core-collapse supernova: A supernova caused by the gravitational collapse of a massive star’s core. Type II events are a major observational class of core-collapse supernovae.
Hydrogen spectral series: Families of emission or absorption lines produced by transitions between energy levels in hydrogen atoms. Hydrogen lines in the supernova spectrum provide the defining observational clue.
SN 1987A: A supernova that exploded in the Large Magellanic Cloud in 1987 and was observed across the electromagnetic spectrum. It provided unusually rich evidence about a Type II explosion and its progenitor.
Type Ib supernova: A core-collapse supernova whose spectrum lacks hydrogen but shows helium. It marks the stripped-envelope outcome opposite to the hydrogen-rich Type II class.
Iron-core collapse: The rapid gravitational contraction of an iron-rich stellar core after fusion can no longer support it. It initiates the explosion in the usual massive-star pathway to a Type II supernova.
Stellar evolution: The changes in a star’s structure, composition, and luminosity over its lifetime. The progenitor’s evolutionary history determines whether it retains a hydrogen envelope at collapse.
SN 1993J: A 1993 supernova in the galaxy M81 that showed hydrogen early and later developed helium-rich spectra. Its changing spectrum illustrates the boundary between hydrogen-rich and stripped-envelope classifications.
Type Ic supernova: A core-collapse supernova whose spectrum lacks strong hydrogen and helium lines. Its progenitor has lost more of its outer layers than a typical Type II progenitor.
Core-collapse shock wave: A shock formed when an infalling stellar core rebounds and encounters material still collapsing inward. Its revival and passage through the star help eject the hydrogen envelope.
Red supergiant: A cool, luminous, highly expanded star with a large radius and an extended outer atmosphere. Many observed Type II progenitors are red supergiants with substantial hydrogen envelopes.

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