Neutron stars capture dark matter efficiently. The kinetic energy transferred
during capture heats old neutron stars in the local galactic halo to
temperatures detectable by upcoming infrared telescopes. We derive the
sensitivity of this probe in the framework of effective operators. For dark
matter heavier than a GeV, we find that neutron star heating can set limits on
the effective operator cutoff that are orders of magnitude stronger than
possible from terrestrial direct detection experiments in the case of
spin-dependent and velocity-suppressed scattering.