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Type Ia supernovae (SNe Ia), thermonuclear explosions of carbon-oxygen white dwarfs (CO-WDs), are currently the best cosmological "standard candles", but the triggering mechanism of the explosion is unknown. It was recently shown that the rate of head-on collisions of typical field CO-WDs in triple systems may be comparable to the SNe Ia rate. Here we provide evidence supporting a scenario in which the majority of SNe Ia are the result of such head-on collisions of CO-WDs. In this case, the nuclear detonation is due to a well understood shock ignition, devoid of commonly introduced free parameters such as the deflagration velocity or transition to detonation criteria. By using two-dimensional hydrodynamical simulations with a fully resolved ignition process, we show that zero-impact-parameter collisions of typical CO-WDs with masses 0. 5-1\, M_ result in explosions that synthesize ^56Ni masses in the range of 0. 1-1\, M_, spanning the wide distribution of yields observed for the majority of SNe Ia. All collision models yield the same late-time (>60 days since explosion) bolometric light curve when normalized by ^56Ni masses (to better than 30\%), in agreement with observations. The calculated widths of the ^56Ni-mass-weighted-line-of-sight velocity distributions are correlated with the calculated ^56Ni yield, agreeing with the observed correlation. The strong correlation, shown here for the first time, between ^56Ni yield and total mass of the colliding CO-WDs (insensitive to their mass ratio), is suggestive as the source for the continuous distribution of observed SN Ia features, possibly including the Philips relation.
Kushnir et al. (Mon,) studied this question.