Grain growth during protostellar disc formation

Recent observations indicate that mm/cm-sized grains may exist in the embedded protostellar disks. How such large grow from micron size (or less) earliest phase of star formation remains relatively unexplored. In this study we take a first step to model grain growth environment, using two-dimensional (2D axisymmetric) radiation hydrodynamic and simulations. We show calculations can be greatly simplified by "terminal velocity approximation", where dust drift relative gas is proportional its stopping time, which size. find grain-grain collision size-dependent terminal alone too slow convert significant fraction initially micron-sized into mm/cm sizes during deeply Class 0 phase. Substantial achieved when speed enhanced factor 4. The above below disk midplane enables settle faster towards midplane, increases local dust-to-gas ratio, which, turn, speeds up further there. needed enhancement unclear, although turbulence strong possibility deserves exploration.