We study the circumstances under which first collisions occur in young and dense star clusters. The initial conditions for our direct N-body simulations are chosen such that the clusters experience core collapse within a few million years, before the most massive stars have left the main-sequence. It turns out that the first collision is typically driven by the most massive stars in the cluster. Upon arrival in the cluster core, by dynamical friction, massive stars tend to form binaries. The enhanced cross section of the binary compared to a single star causes other stars to engage the binary. A collision between one of the binary components and the incoming third star is then mediated by the encounters between the binary and other cluster members. Due to the geometry of the binary-single star engagement the relative velocity at the moment of impact is substantially different than in a two-body encounter. This may have profound consequences for the further evolution of the collision product.

Publication Date



This is a pre-copyedited, author-produced version of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record:

E. Gaburov, A. Gualandris, S. Portegies Zwart; On the onset of runaway stellar collisions in dense star clusters – I. Dynamics of the first collision, Monthly Notices of the Royal Astronomical Society, Volume 384, Issue 1, 11 February 2008, Pages 376–385

is available online at: https://doi.org/10.1111/j.1365-2966.2007.12731.x

Also archived in arXiv:0707.0406 v2 Dec 5, 2007

Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works in February 2014.

Document Type


Department, Program, or Center

School of Physics and Astronomy (COS)


RIT – Main Campus