The End of the MACHO Era: Limits on Halo Dark Matter from Stellar Halo Wide Binaries

Abstract

We simulate the evolution of halo wide binaries in the presence of MAssive Compact Halo Objects (MACHOs) and compare our results to the sample of wide binaries of Chaname & Gould (2003). The observed distribution is well fit by a single power law for angular separation, 3.5" < theta < 900", whereas the simulated distributions show a break in the power law whose location depends on the MACHO mass and density. This allows us to place upper limits on MACHO density as a function of their assumed mass. At the 95% confidence level, we exclude MACHOs with mass M > 43Msun at the standard local halo density rho_H. This all but removes the last permitted window for a full MACHO halo for masses M > 10^{-7.5}Msun.