Incomplete carbon-oxygen detonation in Type Ia supernovae

TL;DR

This study investigates incomplete carbon-oxygen detonations in Type Ia supernovae, revealing their extended lengths, potential instability, and implications for supernova explosion dynamics and observations.

Contribution

It provides new insights into the properties and stability of incomplete C-detonations at low densities, challenging previous assumptions of complete burning.

Findings

C-detonation length is 30-100 times greater than previously estimated.

Decreased nuclear energy release affects detonation stability.

C-detonations may be unstable and re-ignite periodically.

Abstract

Incomplete carbon-oxygen detonation with reactions terminating after burning of 12C in the leading 12C + 12C reaction (C-detonation) may occur in the low density outer layers of white dwarfs exploding as Type Ia supernovae (SNIa). Previous studies of carbon-oxygen detonation structure and stability at low densities were performed under the assumption that the "velocity" of a detonation wave derives from complete burning of carbon and oxygen to iron. In fact, at densities <10^6 g/cm3 the detonation in SNIa may release less than a half of the available nuclear energy. In this paper we study basic properties of such detonations. We find that the length of an unsupported steady-state C-detonation is 30-100 times greater than previously estimated, and that the decreased energy has a drastic effect on the detonation stability. In contrast to complete detonations which are one-dimensionally stable, C-detonations may be one-dimensionally unstable and propagate by periodically re-igniting themselves via spontaneous burning. The re-ignition period at rho < 10^6 g/cm3 is estimated to be greater than the time-scale of a SNIa explosion. This suggests that propagation and quenching of C-detonations at these densities could be affected by the instability. Potential observational implications of this effect are discussed.