Direct Formation of Planetary Embryos in Self-Gravitating Disks

Planet formation in self-gravitating disks typically focuses on the rapid collapse (fragmentation) of dense gas in the disk into gas giant planets. This is particularly effective at larger distances where the disk is cool. Therefore, fragmenting disks are often used to explain direct imaging observations of gas giant planets at wide orbital separations. While the gas dominates the mass budget of a self-gravitating disk, the dust can concentrate into dense filaments when the disk is turbulent but does not fragment. Concentration occurs through the aerodynamic drag of the particles with respect to the gas and leads to density enhancements within the gas spirals. At these densities, the dust can gravitationally collapse into bound clouds or clumps which can be seeds of planet formation. We conduct 3D simulations of dusty self-gravitating disks to investigate the disk conditions and dust particle parameters which lead to the formation of these dense dust clumps. We find that these clumps can be up to several Earth masses in size and their formation is roughly consistent with a criterion where turbulent diffusion of the dust counters the dust self-gravity