tokens: of the cluster will change with the cluster properties. For a massive cluster or for a compact cluster the binding energy will be higher and hence the formation of the SMS would be more favourable. On the 5 Myr time-scale explored in our simulations, supernova feedback is also expected to become relevant. With the typical energy of 10 51 erg for a core-collapse supernova, it is clear that one such event will expel the gas and terminate the accretion, if it has not stopped already (either due to gas expulsion by stellar winds or as the accretion process may have depleted the gas). In future work, it will be important to study detailed gas dynamics where the kinetic energy deposition of winds as well as the supernova feedback is taken into account. 5 SUMMARY AND DISCUSSION In this work, we explored the effect of mass-loss due to stellar winds on the final mass of the SMSs, which could be formed via runaway stellar collisions and gas accretion inside NSCs. We find that an SMS of mass could be formed even in a high-metallicity environment for high accretion rates of . For an accretion rate of , the final mass of the SMS for . Whereas for solar metallicity, no SMS can be formed for f Edd = 0.9 and SMSs of masses can be formed for f Edd = 0.7 and 0.5, respectively. For the case of Eddington accretion it will not be possible to form an SMS in the metallicity regime . Finally, for the Bondi–Hoyle accretion scenario, we find that the formation of a SMS will not be possible in the high-metallicity regime of . The interaction of the stellar wind and the gas inside the cluster might play an important role in the evolution of the SMS. The winds from the SMSs have high velocities ∼10 3 km s −1 (Muijres et al. 2012 ), which might exceed the escape velocity from the centre of our modelled star cluster. The SMS in the cluster is close to the centre which results in a high collision rate near the centre due to a shorter relaxation time in the core and an increased collisional cross-section. If the SMS is displaced by collisions, it rapidly sinks back close to the centre via dynamical friction where it may eventually decouple from the remainder of the cluster. This is also known as the Spitzer instability (Spitzer 1969 ). Interestingly, Krause et al. ( 2016 ) have found that for a Salpeter -type mass function the stellar wind cannot remove the gas inside the cluster. Hence, we do not expect the stellar wind to remove gas from the cluster. One of the main caveats of this work is the neglect of the kinetic energy deposition through stellar winds, which could contribute significantly to expel the gas. The latter is likely to create a regime where the growth of a massive object is still inhibited, even though the mass-loss itself from the winds is no longer significant. Below a critical metallicity in the range (, this effect is no longer expected to be relevant; however, supernova feedback may lead to the expulsion of the gas. Another relevant caveat is the
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