R-modes in neutron stars: Theory and observations

TL;DR

This paper reviews the theory of r-mode instabilities in neutron stars, compares it with observations, and explores additional damping mechanisms and potential observational evidence of r-modes in X-ray binaries.

Contribution

It introduces new considerations of damping mechanisms like exotic cores and superfluid vortices to reconcile theory with observations.

Findings

Standard neutron star models are inconsistent with observed data.

Additional damping mechanisms can suppress r-mode instabilities.

Possible detection of r-mode oscillations in X-ray light curves.

Abstract

In this article I will review the theory behind the gravitational wave driven r-mode instability in rapidly rotating neutron stars and discuss which constraints can be derived from observations of spins and temperatures in Low Mass X-ray Binaries. I will discuss how a standard, `minimal' neutron star model is not consistent with the data, and discuss some of the additional physical mechanisms that could reconcile theory with observations. In particular I will focus on additional forms of damping due to exotic cores and on strong mutual friction due to superfluid vortices cutting through superconducting flux tubes, and examine the repercussions these effects could have on the saturation amplitude of the mode. Finally I will also discuss the possibility that oscillations due to r-modes may have been recently observed in the X-ray light curves of two Low Mass X-ray Binaries.