Decoupling of superfluid and normal modes in pulsating neutron stars

TL;DR

This paper demonstrates that pulsations in superfluid neutron stars can be decoupled into separate superfluid and normal mode equations, simplifying modeling and showing suppressed gravitational wave emission from superfluid modes.

Contribution

It introduces a method to split pulsation equations into weakly coupled sets, significantly simplifying the analysis of superfluid neutron star oscillations.

Findings

Decoupling of superfluid and normal modes with small coupling parameter s.

Approximate s=0 provides accurate pulsation spectrum calculations.

Superfluid modes emit less gravitational radiation than normal modes.

Abstract

We show that equations governing pulsations of superfluid neutron stars can be splitted into two sets of weakly coupled equations, one describing the superfluid modes and another one -- the normal modes. The coupling parameter s is small, |s| ~ 0.01-0.05, for realistic equations of state. Already an approximation s=0 is sufficient to calculate the pulsation spectrum within the accuracy of a few percents. Our results indicate, in particular, that emission of gravitational waves from superfluid pulsation modes is suppressed in comparison to that from normal modes. The proposed approach allows to drastically simplify modeling of pulsations of superfluid neutron stars.