Black Holes in Young Star Clusters

Abstract:Searching for distinctive signatures which characterize different formation channels and environments of binary black holes (BBHs), is a crucial step towards the interpretation of current and future gravitational wave detections. In this talk, I will discuss the formation of merging BBHs in young star clusters (YSCs), which are the nursery of massive stars. In particular, I will show the results of a large set of direct N-body simulations of YSCs with large primordial binary fraction, novel population-synthesis prescriptions and fractal initial conditions to mimic the clumpiness of star forming regions. I will discuss the impact of dynamics on the properties of merging BBHs. More than 50% of merging BBHs formed by dynamical exchange in our simulations. BBHs formed via exchanges are significantly more massive and have smaller mass ratios than BBHs formed from primordial binaries. In our simulations, thanks to multiple stellar collisions and dynamical exchanges, we form merging BBHs with members in the pair instability mass gap. We predict that ~5% of all BBH mergers detectable by advanced LIGO and Virgo at their design sensitivity have at least one component in the pair instability mass gap. Intermediate black black holes (IMBHs) with masses up to ~440 Msun form in my simulations via the runaway collision scenario. IMBHs form preferentially in more massive metal poor SCs and they are extremely efficient in coupling with other BHs. Finally, I will present the new simulations I am performing with the brand-new Petar N-body code, to investigate tidal shocking and IMBH formation in massive (10^5-10^6 Msun) SCs.