Turbulent Mixing on Helium-Accreting White Dwarfs

TL;DR

This paper investigates how turbulent mixing during helium accretion onto white dwarfs influences the conditions for Type Ia supernovae, highlighting the role of hydrodynamic instabilities in core-envelope mixing.

Contribution

It introduces semi-analytic and numerical models to analyze turbulent mixing effects, revealing conditions that lead to significant core material mixing into the accreted helium layer.

Findings

Mixing is strongest at high accretion rates and large WD masses.

Up to 50% C/O can be mixed into the helium layer before ignition.

Results suggest mixing influences the properties of resulting supernovae.

Abstract

An attractive scenario for producing Type Ia supernovae (SNe Ia) is a double detonation, where detonation of an accreted helium layer triggers ignition of a C/O core. Whether or not such a mechanism can explain some or most SNe Ia depends on the properties of the helium burning, which in turn is set by the composition of the surface material. Using a combination of semi-analytic and simple numerical models, I explore when turbulent mixing due to hydrodynamic instabilities during the accretion process can mix C/O core material up into the accreted helium. Mixing is strongest at high accretion rates, large white dwarf (WD) masses, and slow spin rates. The mixing would result in subsequent helium burning that better matches the observed properties of SNe Ia. In some cases, there is considerable mixing that can lead to more than 50% C/O in the accreted layer at the time of ignition. These results will hopefully motivate future theoretical studies of such strongly mixed conditions. Mixing also has implications for other types of WD surface explosions, including the so-called .Ia supernovae, the calcium-rich transients (if they arise from accreting WDs), and metal-enriched classical novae.