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MOCCA code for star cluster simulations - III. Stellar-mass black holes in the globular cluster M22

Using a Monte Carlo code, we construct a dynamic evolutionary model of the Galactic globular cluster M22 (NGC6656). The initial conditions are chosen so that, after about 12Gyr of stellar and dynamical evolution, the model is an approximate fit to the surface brightness and velocity dispersion profiles of the cluster, to its mass function, and to the current binary fraction. Depending on the distribution of black hole natal kicks, we predict that the present-day population of stellar-mass black holes ranges from about 40 (no kicks) down to essentially zero (kicks distributed like those of neutron stars). Provided that natal kicks do not eject all new black holes, it is suggested that clusters with a present-day half-mass relaxation time above about 1Gyr are the ones that may still retain an appreciable population of black holes.