X‐ray pulsar emission is caused by mass infalling onto the magnetic polar regions of neutron stars. The collision stopping length caused by nuclear and coulomb collisions is too large for a standing shock to form above a neutron star surface. We show that collisionless excitation of plasma waves can probably produce a stopping length sufficiently small for such a shock to form. We also describe hydrodynamic models of mass infall under steady state conditions. ©1994 American Institute of Physics.