Observational Signatures of SNIa Progenitors, as Predicted by Models

TL;DR

This study models white dwarf evolution through nova cycles, identifying conditions under which they can grow to trigger type Ia supernovae, and predicts observable signatures of these progenitors.

Contribution

It provides the first detailed simulations showing white dwarfs can steadily grow in mass via nova cycles leading to supernovae, with testable observational predictions.

Findings

White dwarfs can grow in mass through nova cycles under specific conditions.

The model predicts observable pre-supernova light curves and ejecta chemistry.

White dwarf instability and explosion occur after reaching critical temperature and composition.

Abstract

A definitive determination of the progenitors of type Ia supernovae (SNIa) has been a conundrum for decades. The single degenerate scenario $-$ a white dwarf (WD) in a semi-detached binary system accreting mass from its secondary $-$ is a plausible path; however, no simulation to date has shown that such an outcome is possible. In this study, we allowed a WD with a near Chandrasekhar mass of $1.4M_\odot$ to evolve over tens of thousands of nova cycles, accumulating mass secularly while undergoing periodic nova eruptions. We present the mass accretion limits within which a SNIa can possibly occur. The results showed, for each parameter combination within the permitted limits, tens of thousands of virtually identical nova cycles where the accreted mass exceeded the ejected mass, i.e. the WD grew slowly but steadily in mass. Finally, the WD became unstable, the maximal temperature rose by nearly two orders of magnitude, heavy element production was enhanced by orders of magnitude and the nuclear and neutrino luminosities became enormous. We also found that this mechanism leading to WD collapse is robust, with WDs in the range $1.0 - 1.38M_\odot$, and an accretion rate of $5*10^{-7}M_\odot/yr$, all growing steadily in mass. These simulations of the onset of a SNIa event make observationally testable predictions about the light curves of pre-SN stars, and about the chemistry of SNIa ejecta.