13 - Non-spherical delayed detonations

Summary

Abstract

Delayed detonations in exploding carbon-oxygen (C-O) white dwarfs, are bound to ignite and propagate in an expanding Rayleigh-Taylor (R-T) unstable region. Therefore, non-spherical detonations are expected to evolve due to a possible off-center ignition and due to the inhomogeneous composition ahead of the detonation front. We examine some of the possible consequences of such non-spherical explosions, using two-dimensional axisymmetric simulations.

We find that the explosion products, namely the amount of energy released and the composition of the burnt material, are rather sensitive to the asphericity. This sensitivity follows from the fact that the expansion speed is not negligible with respect to the detonation speed. With lower transition density we get less Fe group elements, smaller explosion energy and higher asphericity in the distribution of elements. We also show that the delayed detonation cannot directly induce a second detonation in a nearby isolated bubbles or channels of cold fuel. Therefore, pockets of unburnt C-O mixture may survive deep inside the ejecta.

Introduction

The delayed detonation model for Type Ia supernovae assumes that transition from deflagration to detonation occurs during the combustion of a carbon oxygen (C-O) Chandrasekhar mass white dwarf. In order to fit observations, the transition should occur after a significant expansion that reduces the density of the fuel ahead of the front. Traditionally, the transition point is parametrized by a transition density ρ_tr, which is the density ahead of the deflagration front at the transition moment.