Very massive stars in not so massive clusters

Very young star clusters in the Milky Way exhibit a well-defined relation between their maximum stellar mass, m(max), and their mass in stars, M-ecl. A recent study shows that the young intermediate-mass star cluster VVV CL041 possibly hosts a greater than or similar to 80M(circle dot) star, WR62-2, which appears to violate the existence of the m(max)-M-ecl relation since the mass of the star is almost two times higher than that expected from the relation. By performing direct N-body calculations with the same mass as the cluster VVV CL041 (approximate to 3000M(circle dot)), we study whether such a very massive star can be formed via dynamically induced stellar collisions in a binaryrich star cluster that initially follows the m(max)-M-ecl relation. Eight out of 100 clusters form a star more massive than 80M(circle dot) through multiple stellar collisions. This suggests that the VVV CL041 cluster may have become an outlier of the relation because of its early-dynamical evolution, even if the cluster followed the relation at birth. We find that more than half of our model clusters host a merger product as its most massive member within the first 5 Myr of cluster evolution. Thus, the existence of stars more massive than the m(max)-M-ecl relation in some young clusters is expected due to dynamical processes despite the validity of the m(max)-M-ecl relation. We briefly discuss evolution of binary populations in our model.