Stability of interlinked neutron vortex and proton flux tube arrays in a neutron star. II. Far-from-equilibrium dynamics

TL;DR

This paper investigates the complex, far-from-equilibrium dynamics of neutron vortices and proton flux tubes in a neutron star, revealing new vortex behaviors through 3D simulations of decelerating superfluid systems.

Contribution

It introduces a numerical study of vortex-tangle evolution in neutron stars under deceleration, highlighting the effects of pinning strength and magnetic tilt angle.

Findings

Vortex tangles become more complex with increased tilt angle.

Pinning impedes the deceleration of the neutron condensate.

New vortex behaviors are observed in the simulations.

Abstract

The equilibrium configurations of neutron superfluid vortices interacting with proton superconductor flux tubes in a rotating, harmonic trap are non-trivial in general, when the magnetorotational symmetry is broken. A non-zero angle $\theta$ between the magnetic and rotation axes leads to tangled vorticity due to competition between vortex-vortex repulsion and vortex-flux-tube pinning. Here we investigate the far-from-equilibrium behaviour of the vortices, as the trap decelerates, by solving the time-dependent, stochastic, Gross-Pitaevskii equation numerically in three dimensions. The numerical simulations reveal new vortex behaviours. Key geometrical attributes of the evolving vortex tangle are characterised, as is the degree to which pinning impedes the deceleration of the neutron condensate as a function of $\eta$, the pinning strength, and $\theta$. The simulated system is a partial analogue of the outer core of a decelerating neutron star, albeit in a very different parameter regime.