Dissipative processes in superfluid neutron stars

TL;DR

This paper investigates a new damping mechanism called the rocket effect affecting r-mode oscillations in superfluid neutron stars, providing estimates of damping timescales and analyzing the interplay of superfluidity and mutual friction.

Contribution

It introduces the rocket effect as a novel dissipative process influencing r-mode damping in superfluid neutron stars, using a simplified uniform model and a two-fluid approach.

Findings

Rocket effect can efficiently damp countermoving r-modes.

Mutual friction also contributes to damping.

Damping timescales are estimated for different scenarios.

Abstract

We present some results about a novel damping mechanism of r-mode oscillations in neutron stars due to processes that change the number of protons, neutrons and electrons. Deviations from equilibrium of the number densities of the various species lead to the appearance in the Euler equations of the system of a dissipative mechanism, the so-called rocket effect. The evolution of the r-mode oscillations of a rotating neutron star are influenced by the rocket effect and we present estimates of the corresponding damping timescales. In the description of the system we employ a two-fluid model, with one fluid consisting of all the charged components locked together by the electromagnetic interaction, while the second fluid consists of superfluid neutrons. Both components can oscillate however the rocket effect can only efficiently damp the countermoving r-mode oscillations, with the two fluids oscillating out of phase. In our analysis we include the mutual friction dissipative process between the neutron superfluid and the charged component. We neglect the interaction between the two r-mode oscillations as well as effects related with the crust of the star. Moreover, we use a simplified model of neutron star assuming a uniform mass distribution.