Cluster-assisted accretion for massive stars

Gravitational interactions in very young high-density stellar clusters can to some degree change the angular momentum in the circumstellar disks initially surrounding the majority of stars. However, for most stars, the cluster environment alters the angular momentum only slightly. For example, in simulations of the Orion Nebula cluster (ONC), encounters reduce the angular momentum of the disks by 3%-5%, on average, and in the higher density region of the Trapezium by 15%-20%-still a minor loss process. However, in this Letter, it is demonstrated that the situation is very different if one considers high-mass stars only (M* > 10 M-circle dot). Assuming an age of 2 Myr for the ONC, their disks have, on average, a 50%-90% lower angular momentum than primordially. This enormous loss in angular momentum in the disk should result in an equivalent increase in accretion, implying that the cluster environment boosts accretion for high-mass stars, thus making them even more massive.