3D Hydrodynamical Simulations of Helium-ignited Double-degenerate White Dwarf Mergers

The origins of Type Ia supernovae (SNe Ia) are still debated. Some of the leading scenarios involve a double detonation in double white dwarf (WD) systems. In these scenarios, helium shell detonation occurs on top of a carbon-oxygen (CO) WD, which then drives the detonation of the CO core, producing an SN Ia. Extensive studies have been done on the possibility of a double helium detonation, following a dynamical helium mass-transfer phase onto a CO-WD. However, 3D self-consistent modeling of the double-WD system, the mass transfer, and the helium shell detonation have been little studied. Here we use 3D hydrodynamical simulations to explore this case in which a helium detonation occurs near the point of Roche lobe overflow of the donor WD and may lead to an SN Ia through the dynamically driven double-degenerate double-detonation (D6) mechanism. We find that the helium layer of the accreting primary WD does undergo a detonation, while the underlying CO core does not, leading to an extremely rapid and faint nova-like transient instead of a luminous SN Ia event. This failed core detonation suggests that D6 SNe Ia may be restricted to the most massive CO primary WDs. We highlight the nucleosynthesis of the long-lived radioisotope Ti-44 during explosive helium burning, which may serve as a hallmark both of successful as well as failed D6 events, which subsequently detonate as classical double-degenerate mergers.

Automated summary

The origins of Type Ia supernovae (SNe Ia) are still debated. Some leading scenarios involve double detonation in double white dwarf (WD) systems. In this study, 3D hydrodynamical simulations were used to explore the possibility of a helium detonation near the Roche lobe overflow of the donor WD, which may lead to an SN Ia through the D6 mechanism. It was found that the helium layer undergoes a detonation, while the underlying CO core does not, resulting in a rapid and faint nova-like transient instead of a luminous SN Ia event. The nucleosynthesis of Ti-44 during explosive helium burning was highlighted as a potential hallmark for successful or failed D6 events.