Pulsar velocities and dark matter hint at a singlet neutrino

Two astrophysical puzzles, the origin of pulsar velocities and that of dark matter, may have a simultaneous explanation if there exists a sterile neutrino with a mass in the 1-20 keV range and a small mixing (of order 10^{-4}) with the electron neutrino. Although the mixing is too small for direct detection, future observations of the X-ray telescopes, as well as the gravity waves detectors, such as LIGO and LISA, may be able to confirm or rule out the existence of such a neutrino.