Confronting double-detonation sub-Chandrasekhar models with the low-luminosity suppression of Type Ia supernovae

TL;DR

This paper investigates whether the double-detonation model can explain the observed scarcity of low-luminosity Type Ia supernovae, using detailed simulations to assess ignition conditions in white dwarf stars.

Contribution

The study provides the first full-star simulations showing core ignition is guaranteed if helium shell detonation occurs, challenging the idea that double-detonation models naturally suppress low-luminosity supernovae.

Findings

Core ignition is guaranteed if helium shell detonation occurs.

Low-mass white dwarfs are unlikely to have suppressed ignition in the double-detonation model.

The low-luminosity suppression may require different white dwarf mass distributions or multidimensional effects.

Abstract

Type Ia supernovae (SNe Ia) are likely the thermonuclear explosions of carbon-oxygen (CO) white-dwarf (WD) stars, but their progenitor systems remain elusive. Recently, Sharon & Kushnir (2022) used The Zwicky Transient Facility Bright Transient Survey to construct a synthesized $^{56}$Ni mass, $M_\text{Ni56}$, distribution of SNe Ia. They found that the rate of low-luminosity ($M_\text{Ni56}\approx0.15\,M_{\odot}$) SNe Ia is lower by a factor of $\sim10$ than the more common $M_\text{Ni56}\approx0.7\,M_{\odot}$ events. We here show that in order for the double-detonation model (DDM, in which a propagating thermonuclear detonation wave, TNDW, within a thin helium shell surrounding a sub-Chandrasekhar mass CO core triggers a TNDW within the core) to explain this low-luminosity suppression, the probability of a low-mass ($\approx0.85\,M_{\odot}$) WD explosion should be $\sim100$-fold lower than that of a high-mass ($\approx1.05\,M_{\odot}$) WD. One possible explanation is that the ignition of low-mass CO cores is somehow suppressed. We use accurate one-dimensional numerical simulations to show that if a TNDW is able to propagate within the helium shell, then the ignition within the CO core is guaranteed (resolved here for the first time in a full-star simulation), even for $0.7\,M_{\odot}$ WDs, providing no natural explanation for the low-luminosity suppression. DDM could explain the low-luminosity suppression if the mass distribution of primary WDs in close binaries is dramatically different from the field distribution; if the Helium shell ignition probability is suppressed for low-mass WDs; or if multidimensional perturbations significantly change our results.