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

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 used The Zwicky Transient Facility Bright Transient Survey to construct a synthesized Ni-56 mass, M-Ni56, distribution of SNe Ia. They found that the rate of low-luminosity (M-Ni56 approximate to 0.15 M-circle dot) SNe la is lower by a factor of similar to 10 than the more common M-Ni56 approximate to 0.7 M-circle dot 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 (approximate to 0.85 M-circle dot) WD explosion should be similar to 100-fold lower than that of a high-mass (approximate to 1.05 M-circle dot) 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-circle dot 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.

Automated summary

A recent study found that the rate of low-luminosity events in Type Ia supernovae is lower by a factor of 10 compared to high-luminosity events. In order to explain this suppression, the probability of a low-mass white dwarf explosion needs to be 100 times lower than that of a high-mass white dwarf. Possible explanations include suppressed ignition of low-mass white dwarfs.