Constraints on the Dwarf Star Content of Dark Matter

Infrared observations of the halo of the Milky Way show that less than 3% of the dynamically inferred dark matter is due to $0.1M_{\odot }$ stars ($M8\mathrm{}$ dwarfs). Observations of the diffuse light in the rich cluster of galaxies Abell 2029 lead to even stronger limits. Indeed, less than about 1% of the cluster dark matter is due to $0.1M_{\odot }$ stars. Recent observations of microlensing candidates suggest that the dark matter in the halo of the Milky Way might consist of red/brown dwarf stars with masses in the range $0.01M_{\odot }$ to $1.0M_{\odot }$. If so, the mass function of these objects must be sharply peaked just below $0.1M_{\odot }$, the mass marking the onset of hydrogen burning.