What phenomenon is responsible for triggering a Type Ia supernova explosion?

Answer

A white dwarf accreting mass past the Chandrasekhar limit causing runaway carbon fusion.

Type Ia supernovae result from a thermonuclear explosion. This occurs when a white dwarf in a binary system accretes enough material from its companion to surpass a critical mass limit, igniting rapid, explosive carbon fusion throughout its volume.

What phenomenon is responsible for triggering a Type Ia supernova explosion?
starstellar evolutionsupernovamass