Double-detonation sub-Chandrasekhar supernovae: can minimum helium shell masses detonate the core?

TL;DR

This study uses hydrodynamic simulations to show that minimal helium shell detonations on sub-Chandrasekhar white dwarfs almost always trigger core detonations, supporting the double detonation supernova model.

Contribution

It demonstrates through simulations that even very small helium shells can induce core detonations, confirming the robustness of the double detonation scenario for type Ia supernovae.

Findings

Secondary core detonations occur in all simulated models.

Minimal helium shell masses can trigger core detonations.

Core detonations are virtually inevitable once a helium shell detonation occurs.

Abstract

The explosion of sub-Chandrasekhar mass white dwarfs via the double detonation scenario is a potential explanation for type Ia supernovae. In this scenario, a surface detonation in a helium layer initiates a detonation in the underlying carbon/oxygen core leading to an explosion. For a given core mass, a lower bound has been determined on the mass of the helium shell required for dynamical burning during a helium flash, which is a necessary prerequisite for detonation. For a range of core and corresponding minimum helium shell masses, we investigate whether an assumed surface helium detonation is capable of triggering a subsequent detonation in the core even for this limiting case. We carried out hydrodynamic simulations on a co-expanding Eulerian grid in two dimensions assuming rotational symmetry. The detonations are propagated using the level-set approach and a simplified scheme for nuclear reactions that has been calibrated with a large nuclear network. The same network is used to determine detailed nucleosynthetic abundances in a post-processing step. Based on approximate detonation initiation criteria in the literature, we find that secondary core detonations are triggered for all of the simulated models, ranging in core mass from 0.810 up to 1.385 M_solar with corresponding shell masses from 0.126 down to 0.0035 M_solar. This implies that, as soon as a detonation triggers in a helium shell covering a carbon/oxygen white dwarf, a subsequent core detonation is virtually inevitable.