Stability of interlinked neutron vortex and proton flux-tube arrays in a neutron star -- III. Proton feedback

Abstract

The coupled, time-dependent Gross-Pitaevskii and Ginzburg-Landau equations are solved simultaneously in three dimensions to investigate the equilibrium state and far-from-equilibrium, spin-down dynamics of an interpenetrating neutron superfluid and proton type-II superconductor, as an idealized description of the outer core of a neutron star. The simulations generalize previous calculations without the time-dependent Ginzburg-Landau equation, where proton feedback is absent. If the angle $\theta$ between the rotation and magnetic axes does not equal zero, the equilibrium state consists of geometrically complicated neutron vortex and proton flux-tube tangles, as the topological defects pin to one another locally but align with different axes globally. During spin-down, new types of motion are observed. For $\theta =0$, entire vortices pair rectilinearly with flux tubes and move together while pinned. For $\theta \ne 0$, vortex segments pair with segments from one or more flux tubes, and the paired segments move together while pinned. The degree to which proton feedback impedes the deceleration of the crust is evaluated as a function of $\theta$ and the pinning strength, $\eta$. Key geometric properties of vortex-flux-tube tangles, such as filament length, mean curvature, and polarity are analysed. It is found that proton feedback smooths the deceleration of the crust, reduces the rotational glitch sizes, and stabilizes the vortex tangle dynamics. The dimensionless control parameters in the simulations are mutually ordered to match what is expected in a real neutron star, but their central values and dynamics ranges differ from reality by many orders of magnitude due to computational limitations.

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