Constraints on the mass and abundance of black holes in the Galactic halo : the high mass limit

We establish constraints on the mass and abundance of black holes in the Galactic halo by determining their impact on globular clusters which are conventionally considered to be little evolved. Using detailed Monte Carlo simulations, and simple evolutionary models, we argue that black holes with masses Mbh ∼ > (1 − 3)× 10 M⊙ can comprise no more than a fraction fbh ≈ 0.17 of the total halo density at Galactocentric radius R ≈ 8 kpc. This bound arises from requiring stability of the cluster mass function. A more restrictive bound may be derived if we demand that the probability of destruction of any given, low mass (Mc ≈ (2.5 − 7.5) × 10 4 M⊙) globular cluster not exceed 50%; this bound is fbh ∼ 0.025−0.5 at R ≈ 8 kpc. This constraint improves those based on disk heating and dynamical friction arguments as well as current lensing results. At smaller radius, the constraint on fbh strengthens, while, at larger radius, an increased fraction of black holes is allowed.