Dust growth in protoplanetary disks - a comprehensive experimental/theoretical approach

TL;DR

This paper reviews experimental and theoretical models of dust growth in protoplanetary disks, highlighting the limitations of collisional sticking for planetesimal formation and emphasizing collective effects like streaming and gravitational instabilities.

Contribution

It provides a comprehensive review of the emergent collision model and numerical simulations, integrating experimental data with theoretical insights on dust aggregate evolution.

Findings

Dust aggregates grow rapidly to a few centimeters before bouncing dominates.

Low-velocity fragmentation reduces final dust mass but doesn't restart growth.

Direct collisional formation of kilometer-sized planetesimals appears unlikely.

Abstract

More than a decade of dedicated experimental work on the collisional physics of protoplanetary dust has brought us to a point at which the growth of dust aggregates can - for the first time - be self-consistently and reliably modelled. In this article, the emergent collision model for protoplanetery dust aggregates (G\"uttler et al. 2010) as well as the numerical model for the evolution of dust aggregates in protoplanetary disks (Zsom et al. 2010) are reviewed. It turns out that, after a brief period of rapid collisional growth of fluffy dust aggregates to sizes of a few centimeters, the protoplanetary dust particles are subject to bouncing collisions, in which their porosity is considerably decreased. The model results also show that low-velocity fragmentation can reduce the final mass of the dust aggregates but that it does not trigger a new growth mode as discussed previously. According to the current stage of our model, the direct formation of kilometer-sized planetesimals by collisional sticking seems impossible so that collective effects, such as the streaming instability and the gravitational instability in dust-enhanced regions of the protoplanetary disk, are the best candidates for the processes leading to planetesimals.