Direct Numerical Simulations of Type Ia Supernovae Flames. II. The Rayleigh‐Taylor Instability

A Type Ia supernova explosion likely begins as a nuclear runaway near thecenter of a carbon-oxygen white dwarf. The outward propagating flame isunstable to the Landau-Darrieus, Rayleigh-Taylor, and Kelvin-Helmholtzinstabilities, which serve to accelerate it to a large fraction of the speed ofsound. We investigate the Rayleigh-Taylor unstable flame at the transition fromthe flamelet regime to the distributed-burning regime, around densities of$10^7$ g/cc, through detailed, fully resolved simulations. A low Mach number,adaptive mesh hydrodynamics code is used to achieve the necessary resolutionand long time scales. As the density is varied, we see a fundamental change inthe character of the burning--at the low end of the density range theRayleigh-Taylor instability dominates the burning, whereas at the high end theburning suppresses the instability. In all cases, significant acceleration ofthe flame is observed, limited only by the size of the domain we are able tostudy. We discuss the implications of these results on the potential for adeflagration to detonation transition.Comment: submitted to ApJ, some figures degraded due to size constraint