Dust growth by accretion of molecules in supersonic interstellar
  turbulence
  We show that the growth rate of dust grains in cold molecular clouds is
enhanced by the high degree of compressibility of a turbulent, dilute gas. By
means of high resolution (10243) numerical simulations, we confirm the theory
that the spatial mean growth rate is proportional to the gas-density variance.
This also results in broadening of the grain-size distribution (GSD) due to
turbulence-induced variation of the grain-growth rate. We show, for the first
time in a detailed numerical simulation of hydrodynamic turbulence, that the
GSD evolves towards a shape which is a reflection of the gas-density
distribution, regardless of the initial distribution. That is, in case of
isothermal, rotationally forced turbulence, the GSD tends to be a lognormal
distribution. We also show that in hypersonic turbulence, decoupling of gas and
dust becomes important and that this leads to an even further accelerated grain
growth.
