Probing strange stars and color superconductivity by r-mode instabilities in millisecond pulsars

gamma-mode instabilities in rapidly rotating quark matter stars (strange stars) lead to specific signatures in the evolution of pulsars with periods below 2.5 msec, and may explain the apparent lack of very rapid pulsars. Existing data seem consistent with pulsars being strange stars with a normal quark matter phase surrounded by an insulating nuclear crust. In contrast, quark stars in a color-flavor-locked phase are ruled out. Two-flavor color superconductivity is marginally inconsistent with pulsar data.