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The Direct Formation of Planetary Embryos in Self-Gravitating Disks

Presentation #102.236 in the session Poster Session.

Published onJun 20, 2022
The Direct Formation of Planetary Embryos in Self-Gravitating Disks

Giant planets have been discovered at large separations from the central star. A striking number of young circumstellar disks also have gas and/or dust gaps at large orbital separations, indicating the potential population of young planets there. But to form massive planets at large orbital separations quickly through core accretion, an early solid body to seed pebble and gas accretion is desirable. Early protoplanetary disks are likely self-gravitating, and these gravitoturbulent disks have been shown to efficiently concentrate dust within spiral features. Furthermore, the self-gravity of the gas will enhance settling towards the midplane providing more favorable conditions for dust to reach densities necessary for gravitational collapse. We run 3D local hydrodynamical simulations of gravitoturbulent disks with Lagrangian dust particles to determine whether particle and gas self-gravity can lead to the formation of dense solid bodies which can serve as the starting points of later planet formation. When self-gravity between dust particles is included, solids of size St = 0.1 to 1 concentrate within the gravitoturbulent spiral features and collapse under their own self-gravity into dense clumps which can be up to several M in mass. The most efficiently drifting dust size St=1 forms the most massive clouds of particles, while smaller dust particles St=0.1 concentrate up to masses an order of magnitude lower. Dust cloud masses are smaller by a factor of a few but more numerous, when the effect of dust backreaction onto the gas is included. Crucially, gravitational collapse of dust occurs with the formation of spirals, when the gas disk has an instability parameter Q ~ 1.5. This means the formation of solid planetesimals and embryos can happen without the gas disk being massive enough for fragmentation. The existence of large solid bodies at an early stage of the disk can accelerate the planet formation process, particularly at wide orbital separations, and potentially explain planets far away from the central stars and young disks with substructures.

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