Vortex
Pinning and Dynamics in the Neutron Star Crust
Preprint
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 longstanding
question in astrophysics. Previous estimates of
the vortex-``nucleus'' interaction have been
error-prone, being either phenomenological or derived from
tiny differences of large energies of stationary
configurations. 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, leading thus to interstitial vortex pinning, and
characterize the force as a function of the
vortex-nucleus separation.
The effect of a
force perpendicular to the rotation axis of a gyroscope.
Dynamics of the system for times corresponding to small
vortex-nucleus separations for neutron matter density n=0.014
fm^-3 (top) and 0.031 fm^-3 (bottom). Frames from left to right
correspond to times (10,12,14,16)*1000 fm/c. Blue line
indicates the vortex core position extracted from the pairing
gap. Red dot indicates position of the center of mass of
protons. The vector attached to the red dot denotes the
vortex-nucleus force. Vectors attached to the vortex
indicate contributions to the force per unit length.
Projections of the view are shown on sides of the box. Red
dashed lines denote shape of nucleus. By blue triangles (on
XY-plane) we show trajectory of the vortex up to given time is
shown.
The links to movies showing the dynamics of the pinned and
unpinned vortex-nucleus configurations at two different neutron
background densities.
initially unpinned
vortex initially pinned vortex
initially unpinned vortex
initially pinned vortex