Solid Quark Stars?

It is conjectured that cold quark matter with very high baryon density could be in a solid state, and strange stars with low temperatures should thus be solid stars. The speculation could be close to the truth if no peculiar polarization of thermal X-ray emission (as in, e.g., RX J1856) or no gravitational wave in postglitch phases are detected in future advanced facilities or if spin frequencies beyond the critical ones limited by r -mode instability are discovered. The shear modulus of solid quark matter could be ~10 32 ergs cm -3 if the kilohertz quasi-periodic oscillations observed are relevant to the eigenvalues of the center star oscillations.