Direct Formation of Planetary Embryos in Self-gravitating Disks

Abstract

Giant planets have been discovered at large separations from the central star. Moreover, a striking number of young circumstellar disks have gas and/or dust gaps at large orbital separations, potentially driven by embedded planetary objects. To form massive planets at large orbital separations through core accretion within the disk lifetime, however, an early solid body to seed pebble and gas accretion is desirable. Young protoplanetary disks are likely self-gravitating, and these gravitoturbulent disks may efficiently concentrate solid material at the midplane driven by spiral waves. 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, seeding later planet formation. When self-gravity between dust particles is included, solids of size St = 0.1–1 concentrate within the gravitoturbulent spiral features and collapse under their own self-gravity into dense clumps up to several M ⊕ in mass at wide orbits. Simulations with dust that drift most efficiently, St = 1, form the most massive clouds of particles, while simulations with smaller dust particles, St = 0.1, have clumps with masses an order of magnitude lower. When the effect of dust backreaction onto the gas is included, dust clumps become smaller by a factor of a few but more numerous. 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 distant from the central stars and young protoplanetary disks with substructures.

Planetesimal Initial Mass Functions Following Diffusion-regulated Gravitational Collapse

“…We measure radial particle diffusion via (Johansen & Youdin 2007;Youdin & Lithwick 2007;Schreiber & Klahr 2018;Baehr et al 2022)…”

Spirals and Clumps in V960 Mon: Signs of Planet Formation via Gravitational Instability around an FU Ori Star?

“…Finally, the interest in the formation of planetary cores through gravitational instability has been rekindled with the inclusion of solid material in the process of gravitational instability (Baehr et al 2022). The authors found that under conditions specific to different dust sizes, overdensities can collapse and survive to give rise to planetary embryos.…”

Planetesimal Growth in Evolving Protoplanetary Disks: Constraints from the Pebble Supply

“…More massive planetesimals may form via other disk instabilities than the streaming instability, e.g., the secular gravitational instability (Pierens 2021) and the collapse of pebble clouds in gravitationally unstable early disks (Baehr et al 2022). We carried out a similar simulation to Fiducial and inserted a massive planetesimal of mass 0.01 M ⊕ at the beginning.…”

“…This default setup aims at investigating the planetesimal growth and disk evolution in the class II disk phase. Nevertheless, the outcome can differ if the planetesimals form at a much earlier class 0/I phase (Baehr et al 2022). A more massive reservoir of pebbles is present in such earlier disk phases (Jang et al 2022).…”