# Slowing the Spins of Stellar Cores

## TL;DR

This paper investigates the magnetic Tayler instability as a mechanism for angular momentum transport in stellar interiors, providing improved models that match observed core rotation rates across different stellar evolutionary stages.

## Contribution

It introduces a new saturation prescription for the Tayler instability, leading to more effective angular momentum transport in stellar models, aligning theory with observations.

## Key findings

- Models reproduce nearly rigid solar and main sequence star rotation.
- Core rotation rates of red giants during different burning phases are matched.
- White dwarf rotation rates are accurately predicted.

## Abstract

The angular momentum (AM) evolution of stellar interiors, along with the resulting rotation rates of stellar remnants, remains poorly understood. Asteroseismic measurements of red giant stars reveal that their cores rotate much faster than their surfaces, but much slower than theoretically predicted, indicating an unidentified source of AM transport operates in their radiative cores. Motivated by this, we investigate the magnetic Tayler instability and argue that it saturates when turbulent dissipation of the perturbed magnetic field energy is equal to magnetic energy generation via winding. This leads to larger magnetic field amplitudes, more efficient AM transport, and smaller shears than predicted by the classic Tayler-Spruit dynamo. We provide prescriptions for the effective AM diffusivity and incorporate them into numerical stellar models, finding they largely reproduce (1) the nearly rigid rotation of the Sun and main sequence stars, (2) the core rotation rates of low-mass red giants during hydrogen shell and helium burning, and (3) the rotation rates of white dwarfs. We discuss implications for stellar rotational evolution, internal rotation profiles, rotational mixing, and the spins of compact objects.