The r-mode instability in rotating neutron stars
N. Andersson, K. D. Kokkotas
TL;DR
The r-mode instability in rotating neutron stars presents a gravitational-wave driven channel for angular-momentum loss, with the Coriolis-restored r-modes becoming unstable through the Friedman–Schutz (CFS) mechanism. The main approach balances gravitational-radiation growth against viscous and superfluid damping, yielding an instability window in temperature and rotation rate that depends on microphysics, crusts, and possible exotic states. The work highlights potential spin-down of hot young neutron stars and the prospect of detectable gravitational waves with next-generation detectors, while also addressing accreting neutron stars and the need for more detailed, nonlinear, and relativistic modelling. Overall, while the r-mode instability offers a compelling framework for interpreting spin evolution and GW signals, substantial theoretical and computational advances are needed to produce precise, testable predictions.
Abstract
In this review we summarize the current understanding of the gravitational-wave driven instability associated with the so-called r-modes in rotating neutron stars. We discuss the nature of the r-modes, the detailed mechanics of the instability and its potential astrophysical significance. In particular we discuss results regarding the spin-evolution of nascent neutron stars, the detectability of r-mode gravitational waves and mechanisms limiting the spin-rate of accreting neutron stars in binary systems.