A hydrodynamical trigger mechanism for pulsar glitches

The standard explanation for large pulsar glitches involves transfer of angular momentum from an internal superfluid component to the star's crust. This model requires an instability to trigger the sudden unpinning of the vortices by means of which the superfluid rotates. This Letter describes a new instability that may play this role. 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 model is in good agreement with observed glitch data, suggesting that the superfluid r-mode instability may indeed be the mechanism that triggers large pulsar glitches.