Bulk viscosity of strange matter and r-modes in neutron stars

TL;DR

This paper investigates how different forms of bulk viscosity, caused by hyperons and kaon condensates, influence the damping of r-mode instabilities in neutron stars, highlighting the dominant role of hyperons.

Contribution

It provides a comparative analysis of hyperon and kaon condensate bulk viscosities and their effects on neutron star stability, including the impact of superconducting phases.

Findings

Hyperon bulk viscosity is significantly larger than that of kaon condensates.

Hyperon bulk viscosity effectively damps r-mode instabilities.

Superconducting phases suppress hyperon bulk viscosity.

Abstract

We discuss bulk viscosity due to non-leptonic processes involving hyperons and Bose-Einstein condensate of negatively charged kaons in neutron stars. It is noted that the hyperon bulk viscosity coefficient is a few order of magnitude larger than that of the case with the condensate. Further it is found that the hyperon bulk viscosity is suppressed in a superconducting phase. The hyperon bulk viscosity efficiently damps the r-mode instability in neutron stars irrespective of whether a superconducting phase is present or not in neutron star interior.