The statistical properties and early dust evolution of protostellar discs

Matthew R. Bate

We present an analysis of the statistical properties (masses and sizes) of young (ages <100,000 years) protostellar discs and circumbinary discs that are formed in radiation hydrodynamical simulations of star cluster formation, and we compare these to the observed discs of young stars. We find good agreement between the mass and radius distributions obtained from the simulations compared to the mass and radius distributions of the observed discs of Class 0 and Class I protostars. We find that circumbinary discs in the simulations are exceedingly rare around binaries with semi-major axes >100 AU but that most young binaries with separations less than a few AU have a circumbinary disc, in qualitative agreement with observations. We compare the mutual inclination distributions of binary orbital planes and their circumbinary discs and obtain a very similar distribution to that which is observed, with a strong preference for alignment but around 20% with mutual inclinations >45 degrees.

We also present results from simulations examining dust grain coagulation during the very early stages of star and disc formation. We find that early grain growth depends primarily on gas density, with high density regions such as the first hydrostatic core allowing grain growth to sizes in excess of 100 microns even before the stellar core forms. In gravitationally-unstable protostellar discs, differential grain growth results in larger dust grains being found within the spiral arms than in the rest of the disc even at early times when dust migration is negligible.