Deflagration to detonation transition by amplification of acoustic waves in type Ia supernovae

TL;DR

This paper proposes a new mechanism for deflagration to detonation transition in Type Ia supernovae, involving shock formation from amplified sound waves in white dwarf density gradients, potentially explaining how detonations initiate.

Contribution

It introduces a novel shock amplification mechanism driven by sound waves in white dwarf envelopes, with detailed analysis of conditions needed for detonation initiation in supernovae.

Findings

Detonation can be triggered by sound wave amplification at Mach numbers as low as 0.002.

Planar geometry allows easier detonation initiation than spherical geometry due to damping effects.

Small helium atmospheres facilitate detonation initiation at lower perturbation amplitudes.

Abstract

We study a new mechanism for deflagration to detonation transition in thermonuclear supernovae (SNe Ia), based on the formation of shocks by amplification of sound waves in the steep density gradients of white dwarfs envelopes. Given a large enough jump in density a small pressure and velocity perturbation, produced by the turbulent deflagration, turns into a shock down of the gradient, where it will dissipate and heat up the media. With the right frequency and amplitude the heating can be enough to initiate a detonation, which can propagate backward and up the density gradient. We studied planar and spherical geometry. In the planar case we made a parametric study of the frequency and amplitude. We found it possible to obtain a detonation for perturbations down to Mach number M=0.003. In the spherical case, geometrical damping makes it harder to initiate a detonation, but considering a small He atmosphere (<0.01 Msol) makes it possible again to obtain a detonation down to small perturbation (M=0.002). In the context of thermonuclear supernovae, this could be a mean to turn a turbulent flame producing sound waves to a detonation.