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Concept
Carbon detonation
Summary
Carbon detonation or carbon deflagration is the violent reignition of thermonuclear fusion in a white dwarf star that was previously slowly cooling. It involves a runaway thermonuclear process which spreads through the white dwarf in a matter of seconds, producing a type Ia supernova which releases an immense amount of energy as the star is blown apart. The carbon detonation/deflagration process leads to a supernova by a different route than the better known type II (core-collapse) supernova (the type II is caused by the cataclysmic explosion of the outer layers of a massive star as its core implodes).
A white dwarf is the remnant of a small to medium size star (the Sun is an example of these). At the end of its life, the star has burned its hydrogen and helium fuel, and thermonuclear fusion processes cease. The star does not have enough mass to either burn much heavier elements, or to implode into a neutron star or type II supernova as a larger star can, from the force of its own gravity, so it gradually shrinks and becomes very dense as it cools, glowing white and then red, for a period many times longer than the present age of the Universe.
Occasionally, a white dwarf gains mass from another source – for example, a binary star companion that is close enough for the dwarf star to siphon sufficient amounts of matter onto itself; or from a collision with other stars, the siphoned matter having been expelled during the process of the companion's own late stage stellar evolution. If the white dwarf gains enough matter, its internal pressure and temperature will rise enough for carbon to begin fusing in its core. Carbon detonation generally occurs at the point when the accreted matter pushes the white dwarf's mass close to the Chandrasekhar limit of roughly 1.4 solar masses, the mass at which gravity can overcome the electron degeneracy pressure that prevents it from collapsing during its lifetime. This also happens when two white dwarfs merge if the combined mass is over the Chandrasekhar limit, resulting in a type Ia supernova.
Official source
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