My understanding is that there are three competing theories which have the strongest claim on explaining Type Ia supernovae. The classic theory is that a non-wh

My understanding is that there are three competing theories which have the strongest claim on explaining Type Ia supernovae. The classic theory is that a non-white dwarf companion star feeds material onto a white dwarf, which increases its mass. This kicks off a complicated chain of events, some of which may occur over timescales of a thousand years, ultimately culminating in the initiation of fusion reactions (initially Carbon, then Oxygen) in the core of the white dwarf. The fusion reactions release heat, but because the white dwarf is already under electron degeneracy conditions it is unable to increase pressure and expand to moderate the fusion reactions, so instead they are caught in a very strong positive feedback loop. In a matter of seconds the fusion reactions consume all of the Carbon in the star and then begin consuming the Oxygen in the inner core, this process releases more than enough energy to completely unbind the star gravitationally, the star explodes in a supernova. Alternately, it's also possible that a white dwarf star could have more than enough mass to undergo a Type Ia explosion but is kept in check by rapid spinning. As the star ages and the spinning slows down it crosses a boundary where the above events occur. Or, two white dwarfs could instead merge with each other. It's actually likely, in my opinion, that all three models contribute to Type Ia events in nature, but it's currently unknown which variety is the most common cause of such supernovae.