Type Ia Supernova Explosion Mechanism

Not only is the exact nature of Type Ia progenitors uncertain, the manner in which the star explodes is also still a topic of discussion. What is agreed is that as the white dwarf gains mass from its companion, it contracts and increases its temperature and density. As the mass approaches the Chandrasekhar limit of 1.4 solar masses, the temperature and pressure in the interior of the star is such that a burning front is formed, where carbon is fused into iron and nickel almost instantaneously. It is what happens next that astronomers are still investigating.

The most popular theory is that the white dwarf undergoes a delayed detonation, where this burning front is initially subsonic (deflagration) but later becomes supersonic (detonation). The observed explosion energies and the quantities of unburnt carbon and oxygen rule out a pure deflagration scenario, and the fact that the whole star is not burnt to iron and nickel rules out a pure detonation scenario. By combining the two ideas, astronomers can model the explosion energies and the distributions of elements observed in all Type Ia supernovae by altering when the transition from deflagration to detonation occurs.

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