Simulating the Convective Urca Process with Multiple Urca Pairs in a Simmering White Dwarf

TL;DR

This study uses 3D simulations to explore how the convective Urca process affects convection in simmering white dwarfs, revealing its impact on mixing efficiency and boundary structures.

Contribution

It introduces comprehensive 3D simulations incorporating multiple Urca pairs and compares effects with and without the convective Urca process.

Findings

Convective Urca reduces mixing efficiency near the boundary.

The A=23 Urca pair is the most influential in the process.

The convection zone size remains unaffected by Urca processes.

Abstract

Type Ia supernovae are bright thermonuclear explosions of one or more white dwarf stars. The exact origin and explosion mechanism for these supernovae is still poorly understood. In the near-Chandrasekhar mass progenitor model, a simmering phase precedes the explosion. During this simmering phase, central carbon burning heats the core and drives convection. A poorly understood aspect of this phase is the convective Urca process, a linking of weak nuclear reactions and convective mixing. Convective Urca has the potential to alter characteristics of the convection zone and thus alter the evolution of the white dwarf. To study the convective Urca process, we use the low Mach number hydrodynamic code MAESTROeX to run 3D simulations of the convection zone. We build off previous work to implement a more comprehensive carbon burning network and include the A=21, A=23, and A=25 Urca pairs in the simulations. We compare simulations with and without the convective Urca process to isolate the direct effects the process has on the convection zone. We find the convective Urca process reduces the efficiency of convective mixing near the the convective boundary, but does not restrict the size of the convection zone. We additionally find the A=23 Urca pair to be the most important Urca pair to the convective Urca process in these simulations. All together, our results better inform our understanding of this complex phenomena as well as demonstrates the range of potential convective structures, particularly at the convective boundary, of a simmering white dwarf.