Do superfluid instabilities prevent neutron star precession?

TL;DR

This paper investigates whether superfluid instabilities in neutron stars hinder their precession, finding that slow precession remains feasible while fast precession is likely unstable due to these instabilities.

Contribution

It demonstrates that superfluid instabilities can prevent fast precession in neutron stars, challenging previous assumptions about their precession behavior.

Findings

Superfluid instabilities are triggered during neutron star precession.

Slow precession remains consistent with weak vortex coupling.

Fast precession is generally unstable due to superfluid instabilities.

Abstract

We discuss short wavelength (inertial wave) instabilities present in the standard two-fluid neutron star model when there is sufficient relative flow along the superfluid neutron vortex array. We demonstrate that these instabilities may be triggered in precessing neutron stars, since the angular velocity vectors of the neutron and proton fluids are misaligned during precession. The presence of such an instability would render the standard, solid body rotation, model for free precession inconsistent. Our results suggest that the standard (Eulerian) slow precession that results for weak drag between the vortices and the charged fluid (protons and electrons) is not seriously constrained by the existence of the instability. In contrast, the fast precession, which results when vortices are strongly coupled to the charged component, is generally unstable. This implies that fast precession may not be realised in astrophysical systems