The dynamics of dissipative multi-fluid neutron star cores

TL;DR

This paper develops a Newtonian multi-fluid formalism for superfluid neutron star cores, highlighting how dissipative effects influence oscillation damping and gravitational-wave signals, with applications to hyperon and quark matter cores.

Contribution

It introduces a general formalism for dissipative multi-fluid dynamics in neutron star cores, applicable to various astrophysical and laboratory multi-fluid systems.

Findings

Formalism applied to hyperon core with Lambda and Sigma^- hyperons.

Formalism applied to quark matter core with neutral K^0 kaons.

Potential impact on understanding gravitational-wave driven instabilities.

Abstract

We present a Newtonian multi-fluid formalism for superfluid neutron star cores, focussing on the additional dissipative terms that arise when one takes into account the individual dynamical degrees of freedom associated with the coupled "fluids". The problem is of direct astrophysical interest as the nature of the dissipative terms can have significant impact on the damping of the various oscillation modes of the star and the associated gravitational-wave signatures. A particularly interesting application concerns the gravitational-wave driven instability of f- and r-modes. We apply the developed formalism to two specific three-fluid systems: (i) a hyperon core in which both Lambda and Sigma^- hyperons are present, and (ii) a core of deconfined quarks in the colour-flavour-locked phase in which a population of neutral K^0 kaons is present. The formalism is, however, general and can be applied to other problems in neutron-star dynamics (such as the effect of thermal excitations close to the superfluid transition temperature) as well as laboratory multi-fluid systems.