  The nature of the interaction between superfluid vortices and the neutron
star crust, conjectured by Anderson and Itoh in 1975 to be at the heart vortex
creep and the cause of glitches, has been a long-standing question in
astrophysics. Using a qualitatively new approach, we follow the dynamics as
superfluid vortices move in response to the presence of "nuclei" (nuclear
defects in the crust). The resulting motion is perpendicular to the force,
similar to the motion of a spinning top when pushed. We show that nuclei repel
vortices in the neutron star crust, and characterize the force as a function of
the vortex-nucleus separation.
