Microlensing and the Composition of the Galactic Halo

By means of extensive galactic modeling we study the implications of the more than 100 microlensing events that have now been observed for the composition of the dark halo of the Galaxy. Based on the currently published data, including the 2nd year MACHO results, the halo MACHO fraction is less than 60% in most models and the likelihood function for the halo MACHO fraction peaks around 20% - 40%, consistent with expectations for cold dark matter models.