# Enhanced mixing in magnetized fingering convection, and implications for RGB stars

## TL;DR

This paper investigates how vertical magnetic fields influence fingering convection in stellar interiors, revealing that magnetic fields enhance vertical mixing and potentially explain observed discrepancies in RGB star mixing rates.

## Contribution

It provides the first numerical and theoretical analysis of magnetic effects on fingering convection in astrophysical contexts, highlighting enhanced mixing due to magnetic fields.

## Key findings

- Vertical magnetic fields rigidify fingers along the vertical axis.
- Magnetic fields enhance vertical mixing in fingering convection.
- Proposed a simple model linking magnetic effects to stellar mixing rates.

## Abstract

Double-diffusive convection has been well studied in geophysical contexts, but detailed investigations of the regimes characteristic of stellar or planetary interiors have only recently become feasible. Since most astrophysical fluids are electrically conducting, it is possible that magnetic fields play a role in either enhancing or suppressing double-diffusive convection, but to date there have been no numerical investigations of such possibilities. Here we study the effects of a vertical background magnetic field (aligned with the gravitational axis) on the linear stability and nonlinear saturation of fingering (thermohaline) convection, through a combination of theoretical work and direct numerical simulations (DNSs). We find that a vertical magnetic field rigidifies the fingers along the vertical direction which has the remarkable effect of enhancing vertical mixing. We propose a simple analytical model for mixing by magnetized fingering convection, and argue that magnetic effects may help explain discrepancies between theoretical and observed mixing rates in low-mass red giant branch (RGB) stars. Other implications of our findings are also discussed.