Collisional growth conditions for dust aggregates

Collisions between dust aggregates are the key to understand the formation of planetesimals because the collision inevitably takes place in protoplanetary disks. To clarify whether or not dust aggregates can grow through their mutual collisions at relatively high velocities, we carry out more than 4000 runs of three-dimensional numerical simulations of collisions between icy equal-mass clusters formed under ballistic particle-cluster aggregation (BPCA) as well as those of ballistic cluster-cluster aggregation, including offset collisions with various values of the impact parameter. Since our BPCA clusters have a fractal dimension of 3 and a relatively compact structure, their results enable us to determine the criteria for growth and disruption of compressed aggregates at their collisions in protoplanetary disks. The results show that ice dust aggregates are able to grow at collisions with velocities up to 50 m s ^-1, in spite of their initial structures and impact parameters. We also find that the mass of ejecta relative to the total mass of colliding aggregates decreases with increasing the size of the aggregates. These results demonstrate the feasibility of growth and survival for dust aggregates through their mutual collisions with relatively high velocities in protoplanetary disks.