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Andrew Youdin from the Canadian Institute for Theoretical Astrophysics is the scheduled speaker.

Recent years have seen significant advances in our understanding of how planetesimals, solids bigger than a kilometer, first formed. Youdin will describe dynamical processes that compliment the collisional sticking of small grains. Self-gravity can collect a sea of small solids into a gravitationally bound planetesimal, but stirring by turbulent gas is a formidable obstacle. However several processes can concentrate particles in gas disks – both despite and because of turbulence. The most powerful is the streaming instability, mediated by two-way drag forces between solids and gas. Overdense particle clumps can then collapse gravitationally into planetesimals. Numerical simulations demonstrate the viability of these mechanisms. Youdin will discuss outstanding questions and connections to the planetesimal belts in our solar system. Finally he will briefly comment on a different type of gravitational collapse, that of gas disks into giant planets and brown dwarfs. He will discuss whether recently imaged exoplanets could form by this mechanism.