Constraints on White Dwarfs as Galactic Halo Dark Matter

Abstract

Old, cool white dwarf stars have recently been proposed as a candidate for the dark matter in the Galactic halo, following the detection of very faint moving objects in the Hubble Deep Field (HDF) [1]. We describe here an analysis [2] of ground-based proper motion surveys in which nearby dark halo white dwarfs might be present, if they have the colours and absolute magnitudes proposed. Very few such objects have been found, whereas we argue here that many times more would be expected than were found in the HDF if such objects formed a significant fraction of the dark halo. We use this null-result to derive limits on the optical luminosity of stellar, dark matter candidates.