Discovery of large-scale gravitational infall in a massive protostellar cluster

We report Mopra Australia Telescope National Facility (ATNF), Anglo-Australian Telescope and Atacama Submillimeter Telescope Experiment observations of a molecular clump in Carina, BYF73 = G286.21+0.17, which give evidence of large-scale gravitational infall in the dense gas. From the millimetre and far-infrared data, the clump has a mass of ∼2 × 10⁴ M_⊙, luminosity of ∼2-3 × 10⁴ L_⊙ and diameter of ∼0.9 pc. From radiative transfer modelling, we derive a mass infall rate of ∼3.4 × 10^-2 M_⊙ yr^-1. If confirmed, this rate for gravitational infall in a molecular core or clump may be the highest yet seen. The near-infrared K-band imaging shows an adjacent compact H ii 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 that they indicate the ongoing formation of a massive star cluster. We discuss the implications of these data for competing theories of massive star formation.