Vortex Avalanches and Collective Motion in Neutron Stars

TL;DR

This study simulates quantum vortices in neutron stars, revealing avalanche behavior and collective motion, and introduces a predictive model for vortex avalanches using the Magnus force.

Contribution

First simulation demonstrating spatial-temporal vortex avalanches and collective motion in neutron star superfluids using a Gross--Pitaevskii model.

Findings

Vortex avalanches involve 10-20 vortices exiting rapidly.

Avalanches produce glitches and local vorticity voids.

Magnus force predicts avalanche occurrence.

Abstract

We simulate the dynamics of about 600 quantum vortices in a spinning-down cylindrical container using a Gross--Pitaevskii model. For the first time, we find convincing spatial-temporal evidence of avalanching behaviour resulting from vortex depinning and collective motion. During a typical avalanche, about 10 to 20 vortices exit the container in a short period, producing a glitch in the superfluid angular momentum and a localised void in the vorticity. After the glitch, vortices continue to depin and circulate around the vorticity void in a similar manner to that seen in previous point-vortex simulations. We present evidence of collective vortex motion throughout this avalanche process. We also show that the effective Magnus force can be used to predict when and where avalanches will occur. Lastly, we comment on the challenge of extrapolating these results to conditions in real neutron stars, which contain many orders of magnitude more vortices.