A thermodynamic criterion for the formation of Circumplanetary Disks

TL;DR

This study uses advanced 3D simulations to identify thermodynamic conditions, especially cooling times, that determine whether circumplanetary disks or spherical envelopes form around young giant planets.

Contribution

The paper introduces a thermodynamic criterion based on cooling time for the formation of circumplanetary disks in 3D radiation hydrodynamics simulations, highlighting the role of dust dynamics and heating.

Findings

Shorter cooling times promote disk formation with near-Keplerian angular momentum.

Dust settling enhances cooling and supports rotationally supported disks.

Envelope formation occurs when cooling is insufficient for disk development.

Abstract

The formation of circumplanetary disks is central to our understanding of giant planet formation, influencing their growth rate during the post-runaway phase and observability while embedded in protoplanetary disks. We use 3D global multifluid radiation hydrodynamics simulations with the FARGO3D code to define the thermodynamic conditions that enable circumplanetary disk formation around Jovian planets on wide orbits. Our simulations include stellar irradiation, viscous heating, static mesh refinement, and active calculation of opacity based on evolving dust fluids. We find a necessary condition for the formation of circumplanetary disks in terms of a mean cooling time: when the cooling time is at least one order of magnitude shorter than the orbital time scale, the specific angular momentum of the gas is nearly Keplerian at scales of $R_{\rm{Hill}}/3$. We show that the inclusion of multifluid dust dynamics favors rotational support because dust settling produces an anisotropic opacity distribution that favors rapid cooling. In all our models with radiation hydrodynamics, specific angular momentum decreases as time evolves in agreement with the formation of an inner isentropic envelope due to compressional heating. The isentropic envelope can extend up to $R_{\rm{Hill}}/3$ and shows negligible rotational support. Thus, our results imply that young gas giant planets may host spherical isentropic envelopes, rather than circumplanetary disks.