Fluctuations of electrical conductivity: a new source for astrophysical magnetic fields

TL;DR

This paper introduces a novel mechanism where fluctuations in electrical conductivity within a fluid flow can generate and amplify magnetic fields, potentially explaining magnetic phenomena in astrophysical objects like Neptune and Uranus.

Contribution

It presents a new amplification mechanism for magnetic field generation that leverages conductivity fluctuations, bypassing traditional anti-dynamo constraints.

Findings

Conductivity fluctuations can enable dynamo action in simpler flows.

Numerical simulations show temperature-driven conductivity fluctuations amplify large-scale magnetic fields.

The mechanism may explain the tilted magnetic fields of Neptune and Uranus.

Abstract

We consider the generation of magnetic field by the flow of a fluid for which the electrical conductivity is nonuniform. A new amplification mechanism is found which leads to dynamo action for flows much simpler than those considered so far. In particular, the fluctuations of the electrical conductivity provide a way to bypass anti-dynamo theorems. For astrophysical objects, we show through three-dimensional global numerical simulations that the temperature-driven fluctuations of the electrical conductivity can amplify an otherwise decaying large scale equatorial dipolar field. This effect could play a role for the generation of the unusually tilted magnetic field of the iced giants Neptune and Uranus.