Enhanced Rotational Mixing in the Radiative Zones of Massive Stars

TL;DR

This paper demonstrates that rotation-induced anisotropy in massive stars' cores causes stronger meridional flows and mixing in radiative zones, impacting stellar evolution and potentially explaining observed overshoot distances.

Contribution

It reveals that rotation significantly enhances mixing in radiative zones, akin to convective overshooting, with implications for stellar evolution models.

Findings

Enhanced meridional flow in radiative zones due to rotation.

Mixing strength similar to convective overshooting.

Mixing becomes insensitive to rotation rate above a threshold.

Abstract

Convection in the cores of massive stars becomes anisotropic when they rotate. This anisotropy leads to a misalignment of the thermal gradient and the thermal flux, which in turn results in baroclinicity and circulation currents in the upper radiative zone. We show that this induces a much stronger meridional flow in the radiative zone than previously thought. This drives significantly enhanced mixing, though this mixing does not necessarily reach the surface. The extra mixing takes on a similar form to convective overshooting, and is relatively insensitive to the rotation rate above a threshold, and may help explain the large overshoot distances inferred from observations. This has significant consequences for the evolution of these stars by enhancing core-envelope mixing.