Numerically determined transport laws for fingering ("thermohaline") convection in astrophysics

TL;DR

This paper presents the first 3D simulations of astrophysical fingering convection, revealing simple scaling laws for turbulent transport, and concludes that such convection cannot explain certain stellar chemical abundances.

Contribution

It introduces empirically-derived transport laws for fingering convection applicable to astrophysics, based on novel 3D simulation results.

Findings

Established asymptotic scaling laws for turbulent heat and compositional transport.

Fingering convection does not spontaneously form thermocompositional staircases in stellar interiors.

Fingering convection alone cannot account for observed chemical abundances in RGB stars.

Abstract

We present the first three-dimensional simulations of fingering convection performed in a parameter regime close to the one relevant for astrophysics, and reveal the existence of simple asymptotic scaling laws for turbulent heat and compositional transport. These laws can straightforwardly be extrapolated to the true astrophysical regime. Our investigation also indicates that thermocompositional "staircases," a key consequence of fingering convection in the ocean, cannot form spontaneously in the fingering regime in stellar interiors. Our proposed empirically-determined transport laws thus provide simple prescriptions for mixing by fingering convection in a variety of astrophysical situations, and should, from here on, be used preferentially over older and less accurate parameterizations. They also establish that fingering convection does not provide sufficient extra mixing to explain observed chemical abundances in RGB stars.