Constraining crystalline color superconducting quark matter with gravitational-wave data

We estimate the maximum equatorial ellipticity sustainable by compact stars composed of crystalline color-superconducting quark matter. For the theoretically allowed range of the gap parameter Delta, the maximum ellipticity could be as large as 10(-2), which is about 4 orders of magnitude larger than the tightest upper limit obtained by the recent science runs of the LIGO and GEO600 gravitational-wave detectors based on the data from 78 radio pulsars. We point out that the current gravitational-wave strain upper limit already has some implications for the gap parameter. In particular, the upper limit for the Crab pulsar implies that Delta is less than O(20) MeV for a range of quark chemical potential accessible in compact stars, assuming that the pulsar has a mass 1.4M(circle dot), radius 10 km, breaking strain 10(-3), and that it has the maximum quadrupole deformation it can sustain without fracturing.