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

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