Dynamics of dissipative multifluid neutron star cores

Abstract

We present a Newtonian multifluid formalism for superfluid neutron star cores, focusing on the additional dissipative terms which 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 $\ensuremath{\Lambda}$ and ${\ensuremath{\Sigma}}^{\ensuremath{-}}$ hyperons are present and (ii) a core of deconfined quarks in the color-flavor-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 multifluid systems.