Slowly moving massive neutrinos may be responsible for the invisible mass in galactic halos and the missing mass of the universe. Massive neutrinos are expected to decay into lighter neutrinos and uv photons, with lifetimes long on the Hubble scale. The possible detection of these neutrino-decay photons is discussed.

• Received 3 June 1980

DOI:https://doi.org/10.1103/PhysRevLett.45.942