Temperature effects in pulsating superfluid neutron stars

TL;DR

This paper investigates how finite temperatures influence the oscillation modes of superfluid neutron stars, highlighting the importance of temperature-dependent effects on pulsation spectra and damping times.

Contribution

It introduces models that incorporate temperature effects on superfluid regions and entrainment, providing new insights into neutron star pulsation behaviors near critical temperatures.

Findings

Superfluid pulsation modes are undetectable at the star's surface.

Models ignoring temperature dependence of entrainment yield unrealistic results.

Superfluid modes damp faster than normal modes by 1-3 orders of magnitude.

Abstract

We study the effects of finite stellar temperatures on the oscillations of superfluid neutron stars. The importance of these effects is illustrated with a simple example of a radially pulsating general relativistic star. Two main effects are taken into account: (i) temperature dependence of the entrainment matrix and (ii) the variation of the size of superfluid region with temperature. Four models are considered, which include either one or both of these two effects. Pulsation spectra are calculated for these models, and asymptotes for eigenfrequencies at temperatures close to critical temperature of neutron superfluidity, are derived. It is demonstrated that models that allow for the temperature effect (ii) but disregard the effect (i), yield unrealistic results. Eigenfunctions for the normal- and superfluid-type pulsations are analyzed. It is shown that superfluid pulsation modes practically do not appear at the neutron-star surface and, therefore, can hardly be observed by measuring the modulation of the electromagnetic radiation from the star. The e-folding times for damping of pulsations due to the shear viscosity and nonequilibrium modified Urca processes are calculated and their asymptotes at temperatures close to the neutron critical temperature, are obtained. It is demonstrated that superfluid pulsation modes are damped by 1--3 orders of magnitude faster than normal modes.