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Growth and Disruption of Dust Aggregates by Collisions

Growth and disruption process of dust aggregates by their mutual collisions is important for understanding planetesimal formation in protoplanetary disks. We perform numerical simulations of aggregate collisions using two kinds of aggregates of submicrometer-sized spheres. First, we carry out numerical simulations of head-on collisions between aggregates having ballistic cluster-cluster aggregation (BCCA) structures to reveal their compression process. We obtain a scaling law on the compressed structure of the BCCA clusters and find that the compressed aggregates still remain fluffy with a fractal dimension ∼ 2.5. Second, we simulate collisions between aggregates having ballistic particle-cluster aggregation (BPCA) structures to examine their disruption process. Our results show that the BPCA clusters consisting of ice particles are able to grow at collision velocities up to 60 m s, even if offset collisions are taken into account. This supports a scenario of planetesimal formation through collisions of dust aggregates in protoplanetary disks.