= Solution
A <Type Ia supernova> is a thermonuclear disruption associated with a <carbon-oxygen white dwarf> in a binary system. <Electron degeneracy pressure> supports the dense star, and initially depends much less on temperature than an <ideal gas> pressure does. Once carbon burning heats degenerate material, the immediate pressure response is insufficient to produce the usual expansion-and-cooling thermostat. The strongly temperature-sensitive <nuclear reactions> can therefore undergo a <thermonuclear runaway>.
One channel involves <accretion> toward the <Chandrasekhar limit>, about $1.4$ solar masses for a typical electron composition. Other proposed channels involve merging <white dwarfs> or an initial helium-layer detonation that triggers carbon burning below that mass. Thus the <Chandrasekhar limit> motivates an important model, but it is not an assumption that every <Type Ia supernova> has exactly the same progenitor mass or ignition history. Burning carbon and oxygen into more tightly bound nuclei releases enough <nuclear binding energy> to overcome the stellar gravitational binding energy. An ordinary successful event ejects the star rather than leaving the compact core characteristic of a <core-collapse supernova>.
The ejecta contain iron-group material, including radioactive nickel-56, and intermediate-mass elements from incomplete burning. The <radioactively powered Type Ia supernova light curve> is powered largely by the nickel-56 to cobalt-56 to iron-56 decay chain: its energetic products heat the ejecta, and <radiative diffusion> delays the emerging radiation. Near maximum light, ordinary <Type Ia supernovae> show prominent silicon absorption and lack the hydrogen lines defining Type II events. The spectral classification and the thermonuclear mechanism provide complementary descriptions.
The similar progenitors and radioactive power make <Type Ia supernovae> useful <standard candles>, but their peak <luminosities> are not identical. The relation between <light curve> width and peak brightness, together with color corrections, allows standardization for distance measurements. Extinction, composition and explosion diversity still introduce systematic uncertainties. \b[A Type Ia event is a white-dwarf thermonuclear explosion with a radioactively powered light curve; its corrected luminosity makes it a valuable distance indicator.]
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