Dust evolution in protoplanetary accretion disks

The time evolution of dust particles in circumstellar disk-like structures around protostars and young stellar objects was investigated. For the first time, we coupled the dust evolution directly to the evolution of the disk and followed the influence of opacity changes due to collisional aggregation on the dynamics of the disk. For that purpose, we numerically simulated the dynamical evolution of a turbulent protoplanetary accretion disk described by a time-dependent one-dimensional (radial) “alpha” model. Within this model, the growth of dust grains due to coagulation was calculated by solving numerically the non-linear Smoluchowski equation. As physical processes leading to relative velocities between the grains, Brownian motion, turbulence, and drift motion were taken into account. In contrast to other studies, we especially considered particle-cluster agglomeration (PCA) as growth mode but also included clustercluster agglomeration (CCA) into our considerations. For time periods of 100 years and disk radii up to 100 AU, the mass distributions of coagulated dust grains were calculated. From these mass spectra,we determined the correspondingRosselandmean dust opacities. The variations of the dust grain opacity drive changes in the energetic structure of the protoplanetary disk which again influences the accretion process itself. Our results show three evolutionary stages of the PCA process. For CCA particles, there is no dust growth after the disappearance of the smallest grains. The different characteristic timescales for the coagulation at different radii result in the restructuring of the dust region of the protoplanetary disks. Significant changes in the thermal and optical structure of the disk occur.