Constraining phases of quark matter with studies of r-mode damping in neutron stars

TL;DR

This study uses r-mode damping observations in neutron stars to constrain the presence of certain quark matter phases, finding that pure CFL or CFL-K0 phases are inconsistent with rapid rotation data, implying additional damping mechanisms are necessary.

Contribution

It introduces constraints on high-density quark matter phases in neutron stars based on r-mode damping, highlighting the need for interface dissipation mechanisms.

Findings

Pure CFL and CFL-K0 phases are incompatible with observed rapid rotation.

Shear viscosity alone cannot prevent r-mode instability at typical neutron star temperatures.

Additional damping at quark-hadron or nuclear interfaces is required to explain observations.

Abstract

The r-mode instability in rotating compact stars is used to constrain the phase of matter at high density. The color-flavor-locked phase with kaon condensation (CFL-K0) and without (CFL) is considered in the temperature range 10^8K < T <10^{11} K. While the bulk viscosity in either phase is only effective at damping the r-mode at temperatures T > 10^{11} K, the shear viscosity in the CFL-K0 phase is the only effective damping agent all the way down to temperatures T > 10^8 K characteristic of cooling neutron stars. However, it cannot keep the star from becoming unstable to gravitational wave emission for rotation frequencies f ~ 56-11 Hz at T ~ 10^8-10^9 K. Stars composed almost entirely of CFL or CFL-K0 matter are ruled out by observation of rapidly rotating neutron stars, indicating that dissipation at the quark-hadron interface or nuclear crust interface must play a key role in damping the instability.