Strong toroidal magnetic fields sustained by the elastic crust in a neutron star

TL;DR

This paper presents new models of magnetized neutron stars with elastic crusts, showing that the crust's elasticity supports strong, large-scale toroidal magnetic fields in the core, which was not accounted for in previous studies.

Contribution

It introduces solutions for neutron star magnetic fields considering the elastic crust, revealing the crust's role in sustaining strong toroidal magnetic fields throughout the core.

Findings

Toroidal magnetic fields can be sustained in the entire core region.

Elastic crust supports magnetic fields of order 10^{15} G.

Maximum toroidal field strength is proportional to crust thickness.

Abstract

We investigate new solutions for magnetized neutron stars with a barotropic core in magnetohydrodynamic (MHD) equilibrium and a magneto-elastic crust, which was neglected by previous studies concerning stars in MHD equilibrium. The Lorentz force of the barotropic star is purely irrotational and the structures of magnetic fields are constrained. By contrast, a solenoidal component of the Lorentz force exists in the elastic crust and the structures of the magnetic fields are less restricted. We find that the minor solenoidal component in the elastic crust is important for sustaining the strong magnetic field in the core. Unlike previous studies, the toroidal magnetic field exists in the entire region of the core, and we obtain equilibrium states with large toroidal magnetic fields, where the toroidal magnetic energy is larger than the poloidal magnetic energy. The elastic force of the crust sustains an order of $10^{15}~\mathrm{G}$ toroidal magnetic field in the core, and the maximum strength of the toroidal magnetic field is approximately proportional to the crust thickness.