Discovery of Large-Scale Gravitational Infall in a Possible Massive Protostellar Cluster

We report Mopra (ATNF), Anglo-Australian Telescope, and Atacama Submillimeter Telescope Experiment observations of a molecular core in Carina, BY72 = G286.21+0.17, which give evidence of large-scale gravitational infall in the dense gas. From the millimetre and far-infrared data, the core has mass ∼ 5,000 M⊙, luminosity ∼ 2–3×10 4 L⊙, diameter ∼ 0.9 pc, and mass infall rate ∼ 2.4×10 −2 M⊙yr −1. If confirmed, this rate for gravitational infall in a molecular core may be the highest yet seen. The near-infrared K-band imaging shows an adjacent compact HII region and IR cluster surrounded by a shell-like photodissociation region showing H2 emission. At the molecular infall peak, the K imaging also reveals a deeply embedded group of stars with associated H2 emission. The combination of these features is very unusual and we suggest they indicate the ongoing formation of a massive star cluster. We discuss the implications of these data for competing theories of massive star formation.