A → Type I supernova that presents a singly-ionized silicon
(Si II) absorption feature at 6150 Å near peak brightness. Type Ia SNe
are believed to result from mass → accretion to a
carbon-oxygen → white dwarf in a → close binary
system. When the white dwarf mass exceeds the → Chandrasekhar limit,
the → degenerate electron pressure can no
longer support the accumulated mass and the star collapses in a thermonuclear
explosion producing a supernova. The → peak luminosity
of SNe Ia is set by the radioactive decay chain
56Ni → 56Co → 56Fe,
and the observed photometric correlation between the peak luminosity and the
time-scale over which the → light curve decays from its maximum
is understood physically as having both the luminosity and
→ opacity
being set by the mass of 56Ni synthesized in the explosion.
Type Ia supernovae occur in all types of galaxies.
Type Ia SNe are used as → standard candles in determining
cosmological distances, after normalizing their light curves with the
→ Phillips relation.
See also: → type; → supernova.
