  We review severe constraints on asymmetric bosonic dark matter based on
observations of old neutron stars. Under certain conditions, dark matter
particles in the form of asymmetric bosonic WIMPs can be effectively trapped
onto nearby neutron stars, where they can rapidly thermalize and concentrate in
the core of the star. If some conditions are met, the WIMP population can
collapse gravitationally and form a black hole that can eventually destroy the
star. Based on the existence of old nearby neutron stars, we can exclude
certain classes of dark matter candidates.
