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Abstract: Context: Protoplanetary disks are observed to remain dust-rich for up toseveral million years. Theoretical modeling, on the other hand, raises severalquestions. Firstly, dust coagulation occurs so rapidly, that if the small dustgrains are not replenished by collisional fragmentation of dust aggregates,most disks should be observed to be dust poor, which is not the case. Secondly,if dust aggregates grow to sizes of the order of centimeters to meters, theydrift so fast inwards, that they are quickly lost.Aims: We attempt to verify if collisional fragmentation of dust aggregates iseffective enough to keep disks -dusty- by replenishing the population of smallgrains and by preventing excessive radial drift.Methods: With a new and sophisticated implicitly integrated coagulation andfragmentation modeling code, we solve the combined problem of coagulation,fragmentation, turbulent mixing and radial drift and at the same time solve forthe 1-D viscous gas disk evolution.Results: We find that for a critical collision velocity of 1 m-s, assuggested by laboratory experiments, the fragmentation is so effective, that atall times the dust is in the form of relatively small particles. This meansthat radial drift is small and that large amounts of small dust particlesremain present for a few million years, as observed. For a critical velocity of10 m-s, we find that particles grow about two orders of magnitude larger, whichleads again to significant dust loss since larger particles are more stronglyaffected by radial drift.

Author: T. Birnstiel, C.P. Dullemond, F. Brauer

Source: https://arxiv.org/

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