Magnetic Field Evolution in Superconducting Neutron Stars

TL;DR

This paper develops a multi-fluid magnetohydrodynamics framework to understand how superconductivity and superfluidity in neutron star cores alter magnetic field evolution, revealing new timescales and physical effects.

Contribution

It introduces a novel induction equation accounting for superfluid and superconducting components, highlighting the impact of mutual friction on magnetic field dynamics in neutron stars.

Findings

Identification of two distinct magnetic evolution timescales.

Derivation of an induction equation incorporating mutual friction effects.

Discussion of astrophysical implications of modified magnetic dynamics.

Abstract

The presence of superconducting and superfluid components in the core of mature neutron stars calls for the rethinking of a number of key magnetohydrodynamical notions like resistivity, the induction equation, magnetic energy and flux-freezing. Using a multi-fluid magnetohydrodynamics formalism, we investigate how the magnetic field evolution is modified when neutron star matter is composed of superfluid neutrons, type-II superconducting protons and relativistic electrons. As an application of this framework, we derive an induction equation where the resistive coupling originates from the mutual friction between the electrons and the vortex/fluxtube arrays of the neutron and proton condensates. The resulting induction equation allows the identification of two timescales that are significantly different from those of standard magnetohydrodynamics. The astrophysical implications of these results are briefly discussed.