The Formation of Massive Binary Stars

The formation of massive stars in close binary systems is complicated due to their high radiation pressure, the crowded environment and the expected minimum separation for fragmentation being many times greater than the orbital separation. I discuss how massive star formation can be understood as being due to competitive accretion in stellar clusters. Massive binary systems are then formed due to accretion onto wider low-mass systems. The combination of accretion and dynamical interactions with other stars in the cluster then result in producing a close binary system. Tidal and 3-body captures in dense stellar cores can also play a role in forming massive binary systems while stellar mergers of such close binary systems due to interactions may play an important role in overcoming the radiation pressure.