Aims. In this study, we investigate the dynamics of intermediate-mass black hole (IMBH) binaries within nuclear star clusters (NSCs) that contain a population of stellar-mass black holes (BHs). We examine how these stellar and BH populations influence the dynamics of the IMBH binary and, in turn, how the evolving IMBH binary affects the surrounding stellar and BH populations. Methods. We conducted high-resolution N-body simulations of NSCs constructed based on observational parameters from two local dwarf galaxies: NGC205 and NGC404. For the first time, we achieved a star particle mass resolution of 1 M⊙ and a BH mass resolution of 10 M⊙. This level of resolution is crucial for accurately modeling the collisional dynamics of these dense systems. Results. Including stellar-mass BHs within the stellar population significantly influences the IMBH binary dynamics, nearly doubling the sinking rate and halving the merger time. During the initial phase of the inspiral, the IMBH binary disrupts both the stellar and BH cusps. However, the BH cusp quickly regains its steep slope due to its shorter relaxation time and continues to dominate the evolution of the IMBH binary, despite being much less massive than the stellar component. We uncover an interesting mechanism in which BHs first efficiently extract energy from the IMBH binary and then transfer this energy to the surrounding stars, allowing the BHs to spiral back toward the center of the system and restart the process. Our results imply that although stellar-mass BHs are a minor component of a stellar population they can significantly facilitate IMBH growth within NSCs via mergers. We also notice that these dense systems can potentially boost intermediate-mass ratio inspirals (IMRIs) predominantly on radial orbits.

Nuclear star clusters (NSCs) are dense stellar environments located in the center of most galaxies. NSCs are thought to form through two primary methods: through the inspiral of globular clusters (GCs) to the galactic center due to dynamical friction, and through in situ star formation. Recent observations of dwarf elliptical galaxy UGC 7346 suggest that it might be undergoing NSC formation due to the presence of multiple GCs near its photometric center. We perform direct N-body simulations of nine GCs belonging to UGC 7346’s GC system to investigate whether their eventual infall to the galactic center would result in the formation of an NSC. Our simulations indicate that GCs' inspiral leads to the formation of a central stellar overdensity relative to the background profile of the host galaxy within ∼1.5 Gyr, corresponding to an NSC with a typical mass of (4.1–4.5) × 10⁵ M⊙. Several key structural parameters of the newly formed NSC, including the Sérsic index, effective radius, and central stellar density, lie well within the range observed for NSCs. We also test a hypothetical scenario in which some of the infalling GCs have larger masses (M ∼ 10⁶M⊙), resulting in the formation of a more massive NSC whose mass and size are more consistent with observations. Our results suggest that the inspiral of GCs is a viable channel for assembling a significant mass in the shape of NSCs in the centers of dwarf galaxies and that UGC 7346 will host an NSC at its center in about 2–3 Gyr.