  R-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 (CFL) phase are ruled out. Two-flavor color
superconductivity (2SC) is marginally inconsistent with pulsar data.
