Title: Clumping of mm-cm sized solid particles in the presence of turbulent gas. 

Abstract:

The process of planet formation encompasses more than 13 orders of magnitude in size spanning from micron-meters to ~ 10^5 km. Of the many rungs of the ladder, the intermediate stage involves formation of the smallest gravitationally bounded solid bodies called planetesimals which are kilometer-sized building blocks of fully-fledged planets. The streaming instability (SI) is one of the most promising mechanisms that can efficiently concentrate solid particles to create particle clumps, which could become dense enough to gravitationally collapse to ultimately form planetesimals. However, most of the previous numerical studies for the non-linear SI did not consider external turbulence, which is believed to exist in a protoplanetary disk albeit weak. In this talk, I will present 3D shearing-box simulations of the SI with turbulence driven by our prescribed forcing scheme. Since the turbulence provides an additional diffusion source, it generally prevents concentration of the solid particles and thus weakens or even suppresses the SI. However, depending on initial conditions of the particles, our simulations show that weak turbulence (i.e., rms velocity of ~ 1% of local sound speed) leads to faster SI-clump formation than the simulations without the turbulence. Finally, I will present the criterion for gravitational collapse of the particle clumps that can tell us if particle self-gravity will actually lead to the collapse. 

Physics 3 in person only