  The bulk viscosity in quark matter is sufficiently high to reduce the
effective pressure below the corresponding vapor pressure during density
perturbations in neutron stars and strange stars. This leads to mechanical
instability where the quark matter breaks apart into fragments comparable to
cavitation scenarios discussed for ultra-relativistic heavy-ion collisions.
Similar phenomena may take place in kaon-condensed stellar cores. Possible
applications to compact star phenomenology include a new mechanism for damping
oscillations and instabilities, triggering of phase transitions, changes in
gravitational wave signatures of binary star inspiral, and astrophysical
formation of strangelets. At a more fundamental level it points to the possible
inadequacy of a hydrodynamical treatment of these processes in compact stars.
