NUCLEAR SOLID CRUST ON ROTATING STRANGE QUARK STARS

We calculate in general relativity the thickness, mass, and moment of inertia of the nuclear solid crust that can exist on the surface of a rotating strange quark star suspended out of contact with the quark core by an electric dipole layer on the core surface and the centrifugal force. Aside from the interesting properties of such stars, a particular question of great import to the viability of the strange matter hypothesis is whether strange stars can undergo the observed phenomena of pulsar glitches. We find that the nuclear crust can have a moment of inertia sufficiently large that a fractional change can account for the magnitude of pulsar glitches, even giant glitches. However, before testing a detailed model of the coupling of the crust and quark core, not an easy problem, we are not able to draw the definite conclusion that strange stars can account for all phenomena associated with glitching such as the healing time and recurrence rate. The problem of understanding quakes on compact stars is, afterall, akin to predicting earthquakes. We study the particular sequence of stars, both rotating and stationary, that have the maximum possible crust density, the neutron drip density. The sequence has a minimum mass of about 0.015 M. or about 15 Jupiter masses. Stars near this limit have crusts of thickness tens to hundreds of kilometers and are small and dark and so could be hiding places of baryonic matter.