HEAD-ON COLLISIONS OF WHITE DWARFS IN TRIPLE SYSTEMS COULD EXPLAIN TYPE Ia SUPERNOVAE

Abstract

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 56 Ni 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 56 Ni masses (to better than 30%), in agreement with observations. The calculated widths of the 56 Ni-mass-weighted-line-of-sight velocity distributions are correlated with the calculated 56 Ni yield, agreeing with the observed correlation. The strong correlation, shown here for the first time, between 56 Ni 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.

Supernovae From Direct Collisions of White Dwarfs and the Role of Helium Shell Ignition

“…The simulations were done using the unsplit PPM solver of FLASH in 2D axisymmetric cylindrical coordinates on a grid of size 3.2 × 6.4 10 10 cm using adaptive mesh refinement (AMR). To prevent the production of unreal early detonation that may arise from numerical resolution we applied a limiter approach following Kushnir et al (2013). We made multiple simulations with increased resolution until convergence was reached in the nuclear burning.…”

The white dwarf binary pathways survey – II. Radial velocities of 1453 FGK stars with white dwarf companions from LAMOST DR 4

“…Recently, another possible scenario has been proposed, the so-called core-degenerate channel (Livio & Riess 2003;Kashi & Soker 2011;Soker et al 2013), where a WD merges with the hot core of a massive asymptotic giant branch (AGB) star during or after a common envelope phase. Finally, another possible channel involves the collision of two WDs in a dense stellar environment (Thompson 2011;Katz et al 2011;Kushnir et al 2013;Aznar-Siguán et al 2013). In this scenario either a tertiary star brings two WDs to collide, or the dynamical interaction occurs in a dense stellar system, where such interactions are likely.…”

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“…(e) The WD-WD collision (WWC) scenario (e.g. Kushnir et al 2013). In this scenario, two WDs collide and immediately ignite.…”