Collisional aggregation in turbulent protoplanetary nebula



One of the mechanisms proposed for the formation of planetisimals is the collisional aggregation of dust particles in the turbulent nebula. However, a well-known problem with this idea is that once the aggregates reach a certain size, their collisions become too energetic for them to stick upon impact, and hence they cannot grow beyond this limit. This is the so-called ``bouncing barrier problem''. 

We are working together with a team of astrophysicists from NASA Ames to explore a potential way around the bouncing barrier. This idea is based upon recent discoveries concerning the extreme intermittency of the relative velocity distributions of inertial particles at the small scales of turbulence. This extreme intermittency could enhance the probability of "gentle collisions", for which large aggregates could continue to grow through the bouncing barrier because of the relatively frequent occurance (compared to a Maxwell distribution of particle speeds) of collisions that are gentle enough for the aggregates to stick upon impact.

This work involves high-performance computations of the small-scale dynamics of inertial particles in turbulence, along with the development of simple models and parametrizations. These new models will then be fed into models of planetisimal formation in order to test the hypothesis that small-scale intermittency provides a way around the bouncing barrier, and is effective on astrophysical timescales.