Magnetic field sustained by the elastic force in neutron star crusts

TL;DR

This study explores how elastic forces in neutron star crusts can confine strong magnetic fields, allowing significant magnetic energy storage with implications for crustal stability and magnetic field configurations.

Contribution

It introduces a model showing elastic forces can sustain strong magnetic fields in neutron star crusts, expanding understanding of magnetic energy confinement.

Findings

Magnetic energy > 10^{46} erg can be stored in the crust.

Elastic energy is much less than magnetic energy, around 10^{44}-10^{45} erg.

Crustal shear stress likely causes surface-near breakdowns.

Abstract

We investigate the magneto--elastic equilibrium of a neutron star crust and magnetic energy stored by the elastic force. The solenoidal motion driven by the Lorentz force can be controlled by the magnetic elastic force, so that conditions for the magnetic field strength and geometry are less restrictive. For equilibrium models, the minor solenoidal part of the magnetic force is balanced by a weak elastic force because the irrotational part is balanced by the dominant gravity and pressure forces. Therefore, a strong magnetic field may be confined in the interior, regardless of poloidal or toroidal components. We numerically calculated axially symmetric models with the maximum shear--strain, and found that a magnetic energy $> 10^{46}$ erg can be stored in the crust, even for a normal surface dipole-field-strength ($<10^{13}$ G). The magnetic energy much exceeds the elastic energy ($ 10^{44} -10^{45}$ erg). The shear--stress spatial distribution revealed that the elastic structure is likely to break down near the surface. In particular, the critical position is highly localized at a depth less than 100 m from the surface.