Type Ia supernova diversity: white dwarf central density as a secondary parameter in three-dimensional delayed detonation models

TL;DR

This study uses high-resolution 3D simulations to explore how the central density of white dwarfs influences the diversity of Type Ia supernovae, revealing a correlation between density and iron group element production.

Contribution

The paper introduces a new criterion for the deflagration to detonation transition in 3D supernova models and investigates the impact of central density on supernova nucleosynthesis.

Findings

IGE production increases with central density across supernova brightness levels.

Total 56Ni yield remains roughly constant despite density variations.

Higher density ignitions lead to earlier DDT and increased IGE synthesis.

Abstract

Delayed detonations of Chandrasekhar-mass white dwarfs (WDs) have been very successful in explaining the spectra, light curves, and the width-luminosity relation of spectroscopically normal Type Ia supernovae (SNe Ia). The ignition of the thermonuclear deflagration flame at the end of the convective carbon "simmering" phase in the core of the WD is still not well understood and much about the ignition kernel distribution remains unknown. Furthermore, the central density at the time of ignition depends on the still uncertain screened carbon fusion reaction rates, the accretion history and cooling time of the progenitor, and the composition. We present the results of twelve high-resolution three-dimensional delayed detonation SN Ia explosion simulations that employ a new criterion to trigger the deflagration to detonation transition (DDT). All simulations trigger our DDT criterion and the resulting delayed detonations unbind the star. We find a trend of increasing iron group element (IGE) production with increasing central density for bright, faint, and intermediate SNe. The total 56Ni yield, however, remains more or less constant, even though increased electron captures at high density result in a decreasing 56Ni mass fraction of the IGE material. We attribute this to an approximate balance of 56Ni producing and destroying effects. The deflagrations that were ignited at higher density initially have a faster growth rate of subgrid-scale turbulence. Hence, the effective flame speed increases faster, which triggers the DDT criterion earlier, at a time when the central density of the expanded star is higher. This leads to an overall increase of IGE production, which off-sets the percental reduction of 56Ni due to neutronization.