Collisions versus stellar winds in the runaway merger scenario: Place your bets

The runaway merger scenario is one of the most promising mechanisms to explain the formation of intermediate-mass black holes (IMBHs) in young dense star clusters (SCs). On the other hand, the massive stars that participate in the runaway merger lose mass by stellar winds. This effect is tremendously important, especially at high metallicity. We discuss Nbody simulations of massive (∼ 6 × 104 M) SCs, in which we added new recipes for stellar winds and supernova explosion at different metallicity. At solar metallicity, the mass of the final merger product spans from few solar masses up to ∼ 30 M. At low metallicity (0:01-0:1 Z) the maximum remnant mass is ∼ 250 M, in the range of IMBHs. A large fraction (∼ 0:6) of the massive remnants are not ejected from the parent SC and acquire stellar or black hole companions. Finally, I discuss the importance of this result for gravitational wave detection.