Young massive clusters (YMCs) are dense stellar systems that provide favorable environments for frequent stellar collisions, potentially leading to the formation of very massive stars (VMSs) and seeds of intermediate-mass black holes (IMBHs). In this work, we investigate the role of repeated stellar collisions in YMCs using, a new suite of 18 N-body simulations. Our models span cluster masses of 8 -9, =100-10^ titans 4 5 and half-mass densities ρ_ ̊m h 5, , corresponding to surface densities Σ ∼ 10³- 2. Moreover, they include high primordial binary fractions, consistent with observations of massive stars in young clusters. Overall, our simulations assume cluster properties that are typical of YMCs in the low-redshift Universe. We find that repeated stellar collisions are efficient only in the densest clusters with short relaxation times, and they do not occur in systems with ρ_ pc^ -3 pc^ -2 ̊m h łesssim500, and half-mass relaxation times t_ pc^ -3 ̊m rh Gyr. Rapid mass segregation allows the most massive stars to sink toward the cluster center and create chains of collisions, even in clusters with long core-collapse times. Nevertheless, stellar collision chains are typically triggered by the merger of a primordial binary and most often involve only two collisions. In our simulations, only three VMSs form via repeated stellar collisions and reach masses m_*>330, while the majority have m_*<300, and form via primordial binary mergers. None of these objects represent viable IMBH seeds, as most of them develop helium cores in the (pulsational) pair-instability regime. We formed five IMBHs from single or repeated stellar collisions involving stars at different evolutionary stages, while the dominant IMBH formation channel remains the merger of stellar-mass black holes, which produces twelve IMBHs. For densities and half-mass radii typical of local YMCs, our models show that stellar collision chains are inefficient in producing IMBHs more massive than 140, as most collisionally formed VMSs attain masses that fall in the pair-instability regime.
Mestichelli et al. (Fri,) studied this question.