A new constraint on mean-field galactic dynamo theory

TL;DR

This paper demonstrates that small-scale magnetic fluctuations can suppress galactic dynamo action through a magnetic R"{a}dler effect, reducing the effectiveness of the mean-field dynamo in galaxies.

Contribution

It introduces a new constraint on mean-field galactic dynamo theory by analytically showing how small-scale magnetic fields can inhibit dynamo processes.

Findings

Small-scale magnetic fluctuations suppress galactic dynamo action.

The magnetic R"{a}dler effect reduces the effective alpha effect.

Analytical results based on a generic galaxy model.

Abstract

Appealing to an analytical result from mean-field theory, we show, using a generic galaxy model, that galactic dynamo action can be suppressed by small-scale magnetic fluctuations. This is caused by the magnetic analogue of the R\"{a}dler or $\Omega\times J$ effect, where rotation-induced corrections to the mean-field turbulent transport result in what we interpret to be an effective reduction of the standard $\alpha$ effect in the presence of small-scale magnetic fields.