A new mechanism for saturating unstable r-modes in neutron stars

TL;DR

This paper proposes a novel damping mechanism for neutron star r-modes involving superfluid vortices cutting through superconducting fluxtubes, which could significantly limit mode amplitudes and impact gravitational wave emission.

Contribution

It introduces a new nonlinear dissipation process for neutron star oscillations, specifically affecting r-mode instability saturation.

Findings

The mechanism can produce a lower saturation threshold than previous models.

It suggests neutron star oscillations are less likely to grow beyond critical amplitudes.

Potential implications for gravitational wave signals from neutron stars.

Abstract

We consider a new mechanism for damping the oscillations of a mature neutron star. The new dissipation channel arises if superfluid vortices are forced to cut through superconducting fluxtubes. This mechanism is interesting because the oscillation modes need to exceed a critical amplitude in order for it to operate. Once it acts the effect is very strong (and nonlinear) leading to efficient damping. The upshot of this is that modes are unlikely to ever evolve far beyond the critical amplitude. We consider the effect of this new dissipation channel on the r-modes, that may be driven unstable by the emission of gravitational waves. Our estimates show that the fluxtube cutting leads to a saturation threshold for the instability that can be smaller than that of other proposed mechanisms. This suggests that the idea may be of direct astrophysical relevance.