Pierfrancesco Di Cintio

ISC-CNR & INAF OAA

Multiparticle collision simulations of intermediate mass black holes in globular cluster

We recently introduced a new method for simulating collisional gravitational N-body systems with approximately linear time scaling on N. Our method is based on the Multi-Particle Collision (MPC) scheme, previously applied in Fluid Dynamics and Plasma Physics. We are able to simulate globular clusters with a realistic number of stellar particles (at least up to several times 106) on a standard workstation. We simulate clusters hosting an intermediate mass black hole (IMBH), probing a broad range of BH-cluster and BH–average-star mass ratios, virtually unrestricted by computational constraints. We aim at finding a connection between the central velocity dispersion and the mass of the IMBH, while also investigating anisotropy and the IMBH wander motion. We set up a grid of hybrid particle-in-cell–multiparticle collision (MPC) N-body simulations using our implementation of the MPC method, MPCDSS. We find that models with an IMBH undergo core collapse at earlier times, the larger the IMBH mass the shallower, with an approximately constant central density at core collapse. The presence of an IMBH tends to lower the central velocity dispersion. These results hold independently of the mass function of the model. For the models with Salpeter MF we observe that equipartition of kinetic energies is never achieved, even long after core collapse. Orbital anisotropy at large radii appears driven by energetic escapers on radial orbits, triggered by strong collisions with the IMBH in the core. We confirm and expand on several predictions of star cluster evolution before, during, and after core collapse. Such predictions were based on theoretical calculations or relatively small-size direct N-body simulations, which could not freely explore the range of IMBH mass ratios probed here.

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Multiparticle collision simulations of intermediate mass black holes in globular cluster
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