In a cloud of dust: what is going in the turbulent dusty centres of cold molecular clouds?

We present high resolution simulations of homogeneous isothermal hydrodynamic turbulence inside an interstellar molecular cloud (MC), including a multi-disperse population of dust grains. Large grains will decouple from the gas flow, while small grains will tend to follow the motions of the gas. Our simulations confirm that there exist a minimum in the fractal clustering dimension at a specific Stokes number, i.e., grains of a specific size tend to cluster more than grains which are significantly smaller or larger sizes. The clustering efficiency is sufficiently high to expect that coagulation in MCs can be turbulence driven. Due to spatial separation of dust and gas, we also argue that condensation is less effective than in a velocity-coupled case where there is no variation in the gas-to-dust ratio .