Simulated magnetic field expulsion in neutron star cores

TL;DR

This paper presents self-consistent magneto-thermal simulations of neutron star cores, showing that magnetic flux expulsion is negligible and core fields persist long-term, influencing observable surface emissions.

Contribution

It introduces the first comprehensive simulation considering multiple core magnetic forces, revealing their combined negligible effect on flux expulsion and surface observables.

Findings

Core magnetic flux expulsion is negligible over megayear timescales.

Strong core magnetic fields can persist long after crustal fields decay.

Multiple core forces collectively have minimal impact on surface magnetic signatures.

Abstract

The study of long-term evolution of neutron star (NS) magnetic fields is key to understanding the rich diversity of NS observations, and to unifying their nature despite the different emission mechanisms and observed properties. Such studies in principle permit a deeper understanding of the most important parameters driving their apparent variety, e.g. radio pulsars, magnetars, x-ray dim isolated neutron stars, gamma-ray pulsars. We describe, for the first time, the results from self-consistent magneto-thermal simulations considering not only the effects of the Hall-driven field dissipation in the crust, but adding a complete set of proposed driving forces in a superconducting core. We emphasize how each of these core-field processes drive magnetic evolution and affect observables, and show that when all forces are considered together in vectorial form, the net expulsion of core magnetic flux is negligible, and will have no observable effect in the crust (consequently in the observed surface emission) on megayear time-scales. Our new simulations suggest that strong magnetic fields in NS cores (and the signatures on the NS surface) will persist long after the crustal magnetic field has evolved and decayed, due to the weak combined effects of dissipation and expulsion in the stellar core.