Chemical and Dynamical Forces in Building Large Particles in the Disks Around Young Stars

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During the early stages of planet formation, small dust particles stick together to form larger particles. If the particles are smaller than 1 km in size, forces on the surfaces of these particles, called van der Waals forces, are thought to cause the particles to stick together. Other forces, however, can cause bouncing or breaking apart of the smaller particles. The typical van der Waals force is not strong enough to stop these particles from breaking apart. The investigators will study the possibility that particles joining together depend on chemical forces between the grains, not the van der Waals forces, as the chemical forces are stronger than van der Waals forces. The investigators will model the interaction between chemical forces sticking grains together and physical forces breaking grains apart, in a way that represents the early Solar System formation as we now understand it. This project serves the national interest as it advances our knowledge of the early building processes of the Solar System. The investigators will work to include Bridge Program students in this research project, as part of the UCF Physics Department's participation as an APS Bridge Program site, and will also include research results in K - 12 and college-level classes.Most current hypotheses for the formation of planets in protoplanetary disks are based on the accretion of small dust grains into macroscopic dust aggregates. Several barriers have been identified at different stages of planet formation that could lead to bouncing or fragmentation of particles instead of increased sticking together and subsequent growth of particles. At sizes less than ~1km in diameter, surface forces are thought to be responsible for accretion. These forces are typically modeled as van der Waals forces. Experimental results, however, indicate that the typical strength of the van der Waals force is not sufficient to prevent fragmentation during collisions. Consequently, the mechanisms for the initial stages of planet formation remain poorly understood. The investigators describe here a plan to demonstrate how much the forces between particles in protoplanetary disks might depend on the chemical state of the mineral grains. The objective is to model grain interactions and collisions in a chemical environment that is intended to reflect what is known about the early Solar System during the initial stages of planet formation. Preliminary results indicate that the chemical state of grain surfaces plays an extremely important role, and the usual assumption of weak van der Waals forces is often invalid especially when surfaces are not passivated. Atomic-scale simulation results will be used to develop coarse-grained simulation models that can be used to understand collisions between larger aggregates. As part of the UCF Physics Department's participation as an APS Bridge Program site, the investigators will work to mentor several Bridge Program students with the potential to involve them in this research project. They will also include research results in K - 12 and college-level classes.