The Chandrasekhar Limit & Type Ia Supernovae: Structures & Vocabulary

Electron degeneracy cannot support a white dwarf of arbitrarily large mass. The Chandrasekhar limit, near 1.4 solar masses for a cold nonrotating carbon-oxygen white dwarf, marks the approximate mass scale at which relativistic electron degeneracy can no longer maintain hydrostatic support. In interacting binaries, approaching this regime can lead to thermonuclear disruption and a Type Ia supernova.

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.

Relativistic electron degeneracy changes the mass-radius relation as a white dwarf approaches the limiting mass. Candidate Type Ia channels include accretion from nondegenerate companions and mergers or interactions involving two white dwarfs.