In this paper we study the evolution of a primordial black hole binary ( BHB ) in a sample of over 1500 direct-summation N - body simulations of small-and intermediate-size isolated star clusters as proxies of galactic open clusters .
The BHBs have masses in the range of the first LIGO/Virgo detections .
Some of our models show a significant hardening of the BHB in a relatively short time .
Some of them merge within the cluster , while ejected binaries , typically , have exceedingly long merger timescales .
The perturbation of stars around BHB systems is key to induce their coalescence .
The BHBs which merge in the cluster could be detected with a delay of a few years between space detectors , as future LISA , and ground-based ones , due to their relatively high eccentricity .
Under our assumptions , we estimate a BHB merger rate of R _ { mrg } \sim 2 yr ^ { -1 } Gpc ^ { -3 } .
We see that in many cases the BHB triggers tidal disruption events which , however , are not linked to the GW emission .
Open cluster-like systems are , hence , a promising environment for GWs from BHBs and tidal disruptions .