The r-mode instability in strange stars with a crystalline crust

TL;DR

This paper models strange quark stars with a crystalline crust to explain their stability against r-mode instabilities, supporting the existence of quark matter phases and aligning with observed pulsar rotation speeds.

Contribution

It introduces a model of strange stars with a crystalline quark crust that can withstand r-mode heating, providing a new explanation for stable rapid rotation in pulsars.

Findings

Crystalline quark crusts can resist r-mode heating effectively.

Viscous rubbing at the core-crust boundary stabilizes rotation.

Bare strange stars are inconsistent with observed pulsar spins.

Abstract

The r-mode instability, believed to limit the rotation speed of compact stars, can provide empirical confirmation for the existence of stable deconfined phases of quark matter that are predicted by weak coupling calculations in Quantum Chromodynamics. We construct a model for strange quark stars as heavy as 2 solar masses that are made of superconducting quark matter in the bulk and a thin crystalline quark matter crust. This crystalline quark crust is sufficiently robust to withstand r-mode heating and viscous rubbing for realistic mode amplitudes O(10^{-2}), unlike a crust made of neutron-rich nuclei. The dissipation provided by viscous rubbing at the core-crust boundary is both necessary and sufficient to obtain stable rotation speeds that are consistent with the majority of rapidly spinning pulsars in low mass X-ray binaries. Our analysis implies that while bare strange stars are ruled out by the existence of rapidly spinning pulsars, a strange star with a quark matter crust is a distinct possibility.