Zones of Tayler Instability in Stars

TL;DR

This paper develops an analytical criterion for the Tayler instability in stars, incorporating thermal and compositional stratification, and implements it in stellar evolution models to better understand angular momentum transport.

Contribution

It extends the linear stability analysis of the Tayler instability to include both thermal and compositional stratification, providing a practical toggle switch for stellar evolution codes.

Findings

TI suppressed in lower mass stars' hydrogen shell

TI active in higher mass stars' radiative zones

Different wavenumber activity than previously expected

Abstract

The Tayler instability (TI) of toroidal magnetic fields is a candidate mechanism for driving turbulence, angular momentum (AM) transport, and dynamo action in stellar radiative zones. Recently \cite{Skoutnev_2024} revisited the linear stability analysis of a toroidal magnetic field in a rotating and stably stratified fluid. In this paper, we extend the analysis to include both thermal and compositional stratification, allowing for general application to stars. We formulate an analytical instability criterion for use as a ``toggle switch" in stellar evolution codes. It determines when and where in a star the TI develops with a canonical growth rate as assumed in existing prescriptions for AM transport based on Tayler-Spruit dynamo. We implement such a ``toggle switch" in the MESA stellar evolution code and map out the stability of each mode of the TI on a grid of stellar evolution models. In evolved lower mass stars, the TI becomes suppressed in the compositionally stratified layer around the hydrogen burning shell. In higher mass stars, the TI can be active throughout their radiative zones, but at different wavenumbers than previously expected.