We believe type Ia supernovae are direct WD-WD collisions in triple systems

Abstract:

We show that a few percent of moderately hierarchical triple systems consisting of 2 white dwarfs and an additional slightly more distant star, lead to the head on collision of the two white dwarfs. The inner white dwarf binaries have separations of few - few hundreds of AU, typical of observed binaries, implying that the rate of such collisions may be sufficient to account for type Ia supernovae. 2D and preleminary 3D hydrodynamical simulations of such collisions, in which the ignition process is fully resolved, show that several robust observational features including the range of 56^Ni of ~0.1Msun to 1Msun are recovered in this scenario without free parameters.