3D modelling of magneto-thermal evolution of neutron stars: method and test cases

TL;DR

This paper presents the first 3D magneto-thermal evolution simulations of neutron stars, revealing how magnetic instabilities and localized heating create surface hot spots that match recent X-ray observations.

Contribution

It introduces a realistic 3D simulation method for neutron star crustal evolution, including neutrino emission and magnetic instabilities, advancing understanding of surface temperature patterns.

Findings

Resistive tearing instability develops in about a Hall time for initial toroidal fields >10^{15} G.

Crustal failures occur due to magnetic stresses and dissipation-induced temperature increases.

Hot spots form and evolve, resembling observed X-ray hot spot patterns.

Abstract

Neutron stars harbour extremely strong magnetic fields within their solid outer crust. The topology of this field strongly influences the surface temperature distribution, and hence the star's observational properties. In this work, we present the first realistic simulations of the coupled crustal magneto-thermal evolution of isolated neutron stars in three dimensions with account for neutrino emission, obtained with the pseudo-spectral code Parody. We investigate both the secular evolution, especially in connection with the onset of instabilities during the Hall phase, and the short-term evolution following episodes of localised energy injection. Simulations show that a resistive tearing instability develops in about a Hall time if the initial toroidal field exceeds ~$10^{15}$ G. This leads to crustal failures because of the huge magnetic stresses coupled with the local temperature enhancement produced by dissipation. Localised heat deposition in the crust results in the appearance of hot spots on the star surface which can exhibit a variety of patterns. Since the transport properties are strongly influenced by the magnetic field, the hot regions tend to drift away and get deformed following the magnetic field lines while cooling. The shapes obtained with our simulations are reminiscent of those recently derived from NICER X-ray observations of the millisecond pulsar PSR J0030+0451.