The Chandrasekhar Limit & Type Ia Supernovae: Physical Mechanisms

A Type Ia progenitor involves a white dwarf in a binary system gaining or merging mass under conditions that ignite carbon explosively. The precise progenitor channels include single-degenerate and double-degenerate pathways, and observations indicate that more than one route may contribute.

As a white dwarf becomes denser, electron speeds become relativistic and degeneracy pressure grows less effectively with further compression. If carbon ignites under degenerate conditions, rising temperature does not initially cause enough expansion to regulate the reaction. A thermonuclear runaway can burn a large fraction of the star and unbind it.

Type Ia spectra lack strong hydrogen in the defining classification and show products of thermonuclear burning. Their light curves are powered substantially by radioactive nickel and cobalt decay. Observed binary populations, supernova remnants, and nucleosynthetic yields constrain the possible progenitor pathways.

Carbon ignition in degenerate material can run away because pressure initially responds weakly to rising temperature. Nuclear burning then accelerates faster than ordinary expansion can regulate it, potentially unbinding the star.