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

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.

Accepted in Phys.Rev.Lett

References in corpus (2)

• Effects of a radially varying electrical conductivity on 3D numerical dynamos
• Bistability between equatorial and axial dipoles during magnetic field reversals

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• Electrodynamics of turbulent fluids with fluctuating electric conductivity
• Effects of radial conductivity variation on the Ponomarenko dynamo