Quaking neutron stars

Gravitational, magnetic, and superfluid forces can stress the crust of an e volving neutron star. Fracture of the crust under these stresses could affe ct the star's spin evolution and generate high-energy emission. We study th e growth of strain in the crust of a spinning down, magnetized neutron star and examine the initiation of crust cracking (a starquake). In preliminary work in 1998 we studied a homogeneous model of a neutron star. Here we ext end this work by considering a more realistic model of a solid, homogeneous crust a afloat on a liquid core. In the limits of astrophysical interest, our new results qualitatively agree with those from the simpler model: the stellar crust fractures under shear stress at the rotational equator, matte r moves to higher latitudes, and the star's oblateness is reduced. Magnetic stresses favor faults directed toward the magnetic poles. Thus our previou s conclusions concerning the star's spin response still hold; namely, asymm etric redistribution of matter excites damped precession, which could ultim ately lead to an increase in the spin-down torque. Starquakes associated wi th glitches could explain the permanent offsets in period derivative observ ed to follow glitches in at least three pulsars.