Hydrodynamical trigger mechanism for pulsar glitches.

We describe a new instability that may trigger the global unpinning of vortices in a spinning neutron star, leading to the transfer of angular momentum from the superfluid component to the star's crust. The instability, which is associated with the inertial r modes of a superfluid neutron star, sets in once the rotational lag in the system reaches a critical level. We demonstrate that our simple model agrees well with the observed glitch data. This new idea should stimulate work on more detailed neutron star models, which would account for the crustal shear stresses and magnetic field effects we have ignored.