Mesoscale Turbulence in Type Ia Supernova Deflagrations: Buoyancy-Driven Fuel Heating and Prospects for Delayed-Detonations

TL;DR

This study uses high-resolution 3D simulations to investigate mesoscale buoyancy-driven turbulence in Type Ia supernova deflagrations, revealing significant fuel heating that could facilitate the deflagration-to-detonation transition.

Contribution

It provides the first detailed analysis of mesoscale buoyancy-driven turbulence effects on fuel heating in SNe Ia using adaptive mesh refinement simulations.

Findings

Buoyancy-driven adiabatic heating significantly reduces fuel ignition times.

Fuel heating increases with Rayleigh-Taylor instability forcing.

Regions of intense heating are several hundred meters wide.

Abstract

The aim of this work is to characterize the thermodynamic state of fuel mixed into the turbulent flame brush in the context of the Zel'dovich deflagration-to-detonation transition (ZDDT) mechanism of Type Ia supernovae (SNe Ia). We perform a series of three-dimensional computer simulations of thermonuclear deflagrations subject to the Rayleigh-Taylor instability (RTI) for conditions found in model explosions of centrally ignited realistic, Chandrasekhar mass white dwarf progenitors. These conditions correspond to explosion times when the flame reaches low density progenitor regions where DDT is expected to occur. The flame database is constructed using a thickened flame model. High numerical resolution is achieved with the help of the adaptive mesh refinement (AMR) approach allowing, for the first time, to resolve mesoscale buoyancy-driven flame turbulence. The system is evolved to a quasi-steady state, and flow properties in the turbulent region, where turbulence is most isotropic, is analyzed in a co-moving frame of reference. We find evidence for strong buoyancy-driven adiabatic heating of fuel layers adjacent to the flame front. The heating results in a dramatic reduction of fuel ignition times by between $\approx$2 and more than about 5 orders of magnitude. The heating increases with the RTI forcing. The observed shortening of fuel burning timescales suggests a new source of energy is important inside fuel penetrating the flame brush. These regions are up to several hundred meters wide. On the basis of the previous results of turbulent combustion in SNe Ia, preconditioning required by the ZDDT mechanism can occur there.