Constraints on massive black holes as dark matter candidates using Galactic globular clusters

Abstract

This work considers the idea of massive black holes being the constituents of the Galactic dark matter halo. It constrains the maximum black hole mass to $\mbh \sil 5 \times 10^4 \msun$ by examining their influence on the population of globular clusters in our Milky Way. In the adopted halo model, globular clusters are exposed to constant bombardment of halo objects on their orbits through the Galaxy and thus will steadily gain internal energy. Depending on the mass of these halo objects and the structural parameters of the globular clusters, they can be disrupted on time scales of a few billion years and below. These disruption time scales are calculated using a modification of the well known (classical) impulsive approximation and compared with direct N-body simulations of such encounter events to ensure the method works correctly. For a set of ten prototypical globular cluster models and black hole masses ranging from $10^3$ to $10^7\:\msun$, Monte-Carlo-simulations of $10\,000$ encounter histories over the period of 10 billion years were calculated each, at three different galactocentric distances \mbox{$R = 5$}, $10$ and $15\, \kpc$. These data were compared with the real globular cluster population in our Galaxy and used to obtain the above constraint of $\mbh \sil 5 \times 10^4 \msun$.