Chemical Transport and Spontaneous Layer Formation in Fingering Convection in Astrophysics

TL;DR

This paper introduces a new physically-based model for fingering convection in stars, supported by simulations, which explains mixing processes in stellar interiors and can be integrated into stellar evolution codes.

Contribution

The authors develop a novel model for fingering convection in stars, supported by 3D simulations, and provide an algorithm for implementation in stellar evolution software.

Findings

Model aligns with physical principles and simulations

Suggests formation of thermocompositional staircases

Provides a practical algorithm for stellar codes

Abstract

A region of a star that is stable to convection according to the Ledoux criterion may nevertheless undergo additional mixing if the mean molecular weight increases with radius. This process is called fingering (thermohaline) convection and may account for some of the unexplained mixing in stars such as those that have been polluted by planetary infall and those burning helium-3. We propose a new model for mixing by fingering convection in the parameter regime relevant for stellar (and planetary) interiors. Our theory is based on physical principles and supported by three-dimensional direct numerical simulations. We also discuss the possibility of formation of thermocompositional staircases in fingering regions, and their role in enhancing mixing. Finally, we provide a simple algorithm to implement this theory in one-dimensional stellar codes, such as KEPLER and MESA.