  We consider the implications of fermionic asymmetric dark matter for a "mixed
neutron star" composed of ordinary baryons and dark fermions. We find examples,
where for a certain range of dark fermion mass -- when it is less than that of
ordinary baryons -- such systems can reach higher masses than the maximal
values allowed for ordinary ("pure") neutron stars. This is shown both within a
simplified, heuristic Newtonian analytic framework with non-interacting
particles and via a general relativistic numerical calculation, under certain
assumptions for the dark matter equation of state. Our work applies to various
dark fermion models such as mirror matter models and to other models where the
dark fermions have self interactions.
