  An explanation for the large random velocities of pulsars is presented. Like
many other models, we propose that the momentum imparted to the star is given
at birth. The ultimate source of energy is provided by the intense optically
thick neutrino flux that is responsible for radiating the proto-neutron star's
gravitational binding energy during the Kelvin-Helmholtz phase. The central
feature of the kick mechanism is a radiative-driven magnetoacoustic
instability, which we refer to as ``neutrino bubbles.'' Identical in nature to
the photon bubble instability, the neutrino bubble instability requires the
presence of an equilibrium radiative flux as well as a coherent steady
background magnetic field. Over regions of large magnetic flux densities, the
neutrino bubble instability is allowed to grow on dynamical timescales ~ 1ms,
potentially leading to large luminosity enhancements and density fluctuations.
Local luminosity enhancements, which preferentially occur over regions of
strong magnetic field, lead to a net global asymmetry in the neutrino emission
and the young neutron star is propelled in the direction opposite to these
regions. For favorable values of magnetic field structure, size, and strength
as well as neutrino bubble saturation amplitude, momentum kicks in excess of
1000 km/s can be achieved. Since the neutrino-powered kick is delivered over
the duration of the Kelvin-Helmholtz time ~ a few seconds, one expects
spin-kick alignment from this neutrino bubble powered model.
