2023ApJ...945...68T

The structure of dust aggregates affects many aspects of planet formation, such as the dust collision outcome, opacity, and radiation field. The millimeter-wave scattering polarization in protoplanerary disks indicates that dust aggregates have relatively compact structures with a volume-filling factor ≳0.1. In this study, to explain such compact dust aggregates, we examined the compression of dust aggregates in sticking collisions with high mass ratios by performing a large number of N-body simulations of sequential dust collisions for a wide parameter range. Previous N-body simulations reported inefficient compression in equal-mass collisions between large dust aggregates. In contrast, we found that collisions with high mass ratios can compress the dust aggregate much more effectively. We also developed a new compression model that explains our results for sequential collisions with high mass ratios. Finally, we applied the new compression model to dust aggregates in protoplanetary disks and found a possible pathway to create relatively compact dust aggregates that explain the observed millimeter-wave scattering polarization.