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 N-body simulations of
massive (~6x10^4 Msun) 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 Msun. At low
metallicity (0.01-0.1 Zsun) the maximum remnant mass is ~250 Msun, 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.
