Dust Processing during the Gravitational Collapse of Particle Heaps

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In this project we will investigate the fate of the material which is building up planetesimals during the gravitational collapse of heaps of planetesimal precursors (0.1cm - 1m). A very attractive way to form the kilometre sized Planetesimals in the early solar system is the ”Gravoturbulent Fragmentation” of a cloud of relatively small icy and dusty objects. In a nonturbulent e.g. laminar disk sedimentation of particles leads rather to a Kelvin-Helmholtz instability driven turbulence than to a particle layer dense enough for gravitational collapse (Goldreich-Ward instability). Latest studies on the coagulation efficiency of dust aggregates have shown that cm-sized dust aggregates can rapidly form. However, any further growth seems to be inhibited by either the bouncing or the fragmentation barrier. Hence, Johansen et al. (2006a, 2007) came up with a hybrid scenario in which turbulent concentration of depending on the location in the disk millimetre to meter sized icy and dusty material leads to sufficiently large densities in which self gravity dominates over gas drag and the tidal forces of the star, thus a heap of material collapses spontaneously under its own weight into a many kilometre sized planetesimal. In the proposed project we aim to investigate the effect of the collisions during the gravitational fragmentation3 phase. A main question we want to address here, is whether a collisional fragmentation of the solids could stop the collapse and thus diminish or destroy the possibility to form planetesimals from gravitational fragmentation.