Evolution of magnetic deformation in neutron star crust

Abstract

In this study, we examine the magnetic field evolution occurring in a neutron star crust. Beyond the elastic limit, the lattice ions are assumed to act as a plastic flow. The Ohmic dissipation, Hall drift, and bulk fluid velocity driven by the Lorentz force are considered in our numerical simulation. A magnetically induced quadrupole deformation is observed in the crust during the evolution. Generally, the ellipticity decreases as the magnetic energy decreases. In a toroidal-field-dominated model, the sign of the ellipticity changes. Namely, the initial prolate shape tends to become oblate. This occurs because the toroidal component decays rapidly on a smaller timescale than the poloidal dipole component. We find that the magnetic dipole component does not change significantly on the Hall timescale of $\sim 1$Myr for the considered simple initial models. Thus, a more complex initial model is required to study the fast decay of surface dipoles on the abovementioned timescale.