On Sunspot and Starspot Lifetimes

TL;DR

This paper investigates sunspot and starspot lifetimes through magnetic diffusion, showing turbulent diffusivity and supergranule size are key to understanding observed spot durations on the Sun and other stars.

Contribution

It demonstrates that turbulent magnetic diffusivity, linked to supergranule size, explains spot lifetimes and extends solar relations to other stars with larger supergranules.

Findings

Turbulent diffusivity explains sunspot lifetimes.

Supergranule size is crucial for stellar spot lifetime predictions.

Solar and stellar spot lifetimes are consistent with turbulent diffusion models.

Abstract

We consider the lifetimes of spots on the Sun and other stars from the standpoint of magnetic diffusion. While normal magnetic diffusivity predicts lifetimes of sunspots that are too large by at least two orders of magnitude, turbulent magnetic diffusivity accounts for both the functional form of the solar empirical spot-lifetime relation and for the observed sunspot lifetimes, provided that the relevant diffusion length is the supergranule size. Applying this relation to other stars, the value of turbulent diffusivity depends almost entirely on supergranule size, with very weak dependence on other variables such as magnetic field strength and density. Overall, the best observational data for other stars is consistent with the extension of the solar relation provided that stellar supergranule sizes for some stars are significantly larger than they are on the Sun.