The ecology of dense star clusters with binaries

We study the first 100 Myr of the evolution of isolated star clusters with 117965 single stars and 13107 primordial hard binaries. Our calculations include stellar and binary evolution. The early evolution of these clusters can be characterized by three distinct phases, which we dubbed A, B and C. Here phase A lasts for the first similar to 3 Myr and is dominated by two-body relaxation, phase B lasts to about 20-100 Myr and is dominated by stellar mass loss, after that phase C sets in, which again is dominated by two-body relaxation. The presence of the primordial binaries has little effect on these various stages, nor on the other conclusions we draw here. The mass function of the main-sequence stars in the core becomes as flat as x = -1.8 (initial Salpter was x = -2.35), and in the outer 10% (by mass) of the cluster the mass function exponent is as steep as x = -2.6. Over the lifetime of the star cluster; a large number of stellar-mass black holes and neutron stars are formed. Roughly 50%-70% of the black holes are retained by the clusters, whereas the neutron star retention fraction is about 7%-12%. A relatively large fraction of black holes become members of a binary either with another black hole (similar to 40%) or with another stellar companion (similar to 50%). We conclude that in young (but greater than or similar to 50 Myr) star clusters the X-ray binaries with a black hole may outnumber those with a neutron star by about a factor of 3.