TYPE-IA SUPERNOVAE - CONSTRAINTS ON BARYONIC DARK MATTER

We examine models in which the dark matter of galaxy halos is in the form of white dwarfs (WDs). Major constraints, which have been previously neglected, result from the occurrence of Type Ia supernovae, which are the products of merging WDs in binary systems whose orbits decay due to the emission of gravitational wave radiation. The lack of observed supernovae in the outer regions of galaxies, together with the relatively low abundance of iron in the hot, X-ray gas of galactic halos, limit the fraction of binaries to << 1% in extant models of WD-dominated halos, for standard Type Ia parameters. This binary fraction is much smaller than that believed typical for luminous stars, necessitating a further peculiarity in the star-formation process during the formation of the dark halo.