by Holly Capelo
In our experiment in the Göttingen Dilute Gas Stream Facility GDGSF, we
produce a 'wind' which contains very small spherical particles. The density of the wind is 1/100th the density of air at sea level. The particles' sizes range from approximately
70 micrometres (the same as the thickness of a human hair) down to 20 micrometres (about half of the limit of what is visible to the unassisted human eye). When the particles are trapped in
the flow, we use high-resolution cameras to track their positions, to learn if and how the particles may swarm together in the flow and how the particles' group behaviour is different from the
simple dynamics of individual particles.
The spheres in the experiment are analogous to the small grains which are present in the dust- and gas- filled discs around young stars. In such environments, it is believed that particle-gas fluid instabilities, including the streaming instability, play a prominent role in the process of concentrating dust particles to assist in the formation of bigger objects like planetesimals, which are the precursors of planets.
An experimental simulation of collisions between dust aggregates in the early solar system to understand the first steps of planet fomation is beautifully portrayed by an article in the Journal of Visualized Experiments JoVE by
Blum, J., Beitz, E., Bukhari, M., Gundlach, B., Hagemann, J. H., Heißelmann, D., et al. Laboratory Drop Towers for the Experimental Simulation of Dust-aggregate Collisions in the Early Solar System. J. Vis. Exp. (88), e51541, doi:10.3791/51541 (2014).