Low Mach Number Modeling of Type Ia Supernovae. IV. White Dwarf Convection

TL;DR

This paper presents the first 3D full-star simulations of convection in a white dwarf before a Type Ia supernova, revealing dynamic flow structures, gravity waves, and ignition conditions using advanced low Mach number hydrodynamics.

Contribution

It introduces a novel 3D simulation approach for white dwarf convection with a new mapping technique, enabling detailed long-term modeling of supernova ignition.

Findings

Flow dipole orientation changes over time.

Gravity waves develop in the star's outer layers.

Ignition radii vary in the simulations.

Abstract

We present the first three-dimensional, full-star simulations of convection in a white dwarf preceding a Type Ia supernova, specifically the last few hours before ignition. For these long-time calculations we use our low Mach number hydrodynamics code, MAESTRO, which we have further developed to treat spherical stars centered in a three-dimensional Cartesian geometry. The main change required is a procedure to map the one-dimensional radial base state to and from the Cartesian grid. Our models recover the dipole structure of the flow seen in previous calculations, but our long-time integration shows that the orientation of the dipole changes with time. Furthermore, we show the development of gravity waves in the outer, stable portion of the star. Finally, we evolve several calculations to the point of ignition and discuss the range of ignition radii.