Stellar collisions in accreting protoclusters: a Monte Carlo dynamical study

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Abstract

We explore the behaviour of accreting protoclusters with a Monte Carlo dynamical code in order to evaluate the relative roles of accretion, two body relaxation and stellar collisions in the cluster evolution. We corroborate the suggestion of Clarke & Bonnell that the number of stellar collisions should scale as $N^{5/3} \dot M^{2/3}$ (independent of other cluster parameters, where N is the number of stars in the cluster and $\dot M$ the rate of mass accretion) and thus strengthen the argument that stellar collisions are more likely in populous (large N) clusters. We however find that the estimates of Clarke & Bonnell were pessimistic in the sense that we find that more than 99 % of the stellar collisions occur within the post-adiabatic regime as the cluster evolves towards core collapse, driven by a combination of accretion and two-body relaxation. We discuss how the inclusion of binaries may reduce the number of collisions through the reversal of core collapse but also note that it opens up another collisional channel involving the merger of stars within hard binaries; future Nbody simulations are however required in order to explore this issue.