MACHO Project Limits on Black Hole Dark Matter in the 1-30 M☉ Range

We report on a search for long-duration microlensing events toward the Large Magellanic Cloud. We find none and therefore put limits on the contribution of high-mass objects to the Galactic dark matter. At a 95% confidence level, we exclude objects in the mass range of 0.3-30.0 M☉ from contributing more than 4 × 1011 M☉ to the Galactic halo. Combined with earlier results, this means that objects with masses under 30 M☉ cannot make up the entire dark matter halo if the halo is of typical size. For a typical dark halo, objects with masses under 10 M☉ contribute less than 40% of the dark matter.