Type Ia supernova
Within a few seconds of initiation of nuclear fusion, a substantial fraction of the matter in the white dwarf undergoes a runaway reaction, releasing enough energy (1×1044 J)[4] to unbind the star in a supernova explosion.
[5] The Type Ia category of supernova produces a fairly consistent peak luminosity because of the fixed critical mass at which a white dwarf will explode.
[8] When a slowly-rotating[2] carbon–oxygen white dwarf accretes matter from a companion, it can exceed the Chandrasekhar limit of about 1.44 M☉, beyond which it can no longer support its weight with electron degeneracy pressure.
[11] The current view among astronomers who model Type Ia supernova explosions, however, is that this limit is never actually attained and collapse is never initiated.
[13][16] Regardless of the exact details of how the supernova ignites, it is generally accepted that a substantial fraction of the carbon and oxygen in the white dwarf fuses into heavier elements within a period of only a few seconds,[15] with the accompanying release of energy increasing the internal temperature to billions of degrees.
The typical visual absolute magnitude of Type Ia supernovae is Mv = −19.3 (about 5 billion times brighter than the Sun), with little variation.
The theory of this type of supernova is similar to that of novae, in which a white dwarf accretes matter more slowly and does not approach the Chandrasekhar limit.
If the two stars share a common envelope then the system can lose significant amounts of mass, reducing the angular momentum, orbital radius and period.
[22] A second possible mechanism for triggering a Type Ia supernova is the merger of two white dwarfs whose combined mass exceeds the Chandrasekhar limit.
[22] Observations made with NASA's Swift space telescope ruled out existing supergiant or giant companion stars of every Type Ia supernova studied.
The missing radiation indicates that few white dwarfs possess accretion discs, ruling out the common, accretion-based model of Ia supernovae.
Thereafter a close binary system may spend another million years in the mass transfer stage (possibly forming persistent nova outbursts) before the conditions are ripe for a Type Ia supernova to occur.
Previous observations with the Hubble Space Telescope did not show a star at the position of the event, thereby excluding a red giant as the source.
The expanding plasma from the explosion was found to contain carbon and oxygen, making it likely the progenitor was a white dwarf primarily composed of these elements.
Details of the pre-nova moments may help scientists better judge the quality of Type Ia supernovae as standard candles, which is an important link in the argument for dark energy.
Near the time of maximal luminosity, the spectrum contains lines of intermediate-mass elements from oxygen to calcium; these are the main constituents of the outer layers of the star.
The radioactive decay of nickel-56 through cobalt-56 to iron-56 produces high-energy photons, which dominate the energy output of the ejecta at intermediate to late times.
The original correction to standard candle value is known as the Phillips relationship[49] and was shown by this group to be able to measure relative distances to 7% accuracy.
[50] The cause of this uniformity in peak brightness is related to the amount of nickel-56 produced in white dwarfs presumably exploding near the Chandrasekhar limit.
[51] The similarity in the absolute luminosity profiles of nearly all known Type Ia supernovae has led to their use as a secondary standard candle in extragalactic astronomy.
subclass that exhibits particularly strong iron absorption lines and abnormally small silicon features,[59] and 1991bg-likes, an exceptionally dim
[60] Despite their abnormal luminosities, members of both peculiar groups can be standardized by use of the Phillips relation, defined at blue wavelengths, to determine distance.
