Strange stars as persistent sources of gravitational waves

Andersson, N., Jones, D.I. and Kokkotas, K.D. (2002) Strange stars as persistent sources of gravitational waves. Monthly Notices of the Royal Astronomical Society, 337 (4), 1224-1232. (doi:10.1046/j.1365-8711.2002.05837.x).

Abstract

We investigate the relevance of the gravitational-wave driven r-mode instability for strange stars. We find that the unstable r-modes affect strange stars in a way that is quite distinct from the neutron star case. For accreting strange stars, we show that the onset of r-mode instability does not lead to the thermo-gravitational runaway that is likely to occur in neutron stars. Instead, the strange star evolves towards a quasi-equilibrium state on a time-scale of about a year. This mechanism could thus explain the clustering of spin frequencies inferred from kHz quasi-periodic oscillation data in low-mass X-ray binaries. For young strange stars, we show that the r-mode driven spin-evolution is also distinct from the neutron star case. In a young strange star, the r-mode undergoes short cycles of instability during the first few months. This is followed by a quasi-adiabatic phase where the r-mode remains at a small, roughly constant, amplitude for thousands of years. Another distinguishing feature from the neutron star case is that the r-modes in a strange star never grow to amplitudes of the order of unity. Our results suggest that the r-modes in a strange star emit a persistent gravitational-wave signal that should be detectable with large-scale interferometers given an observation time of a few months. If detected, these signals would provide unique evidence for the existence of strange stars, which would put useful constraints on the parameters of quantum chromodynamics.

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Contributors

Author: N. Andersson

Author: D.I. Jones

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