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 Δ, 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 Δ 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_, radius 10 km, breaking strain 10^-3, and that it has the maximum quadrupole deformation it can sustain without fracturing.
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Lap-Ming Lin (2007) studied this question.