Circumplanetary disks around young giant planets: a comparison between core-accretion and disk instability

TL;DR

This study uses hydrodynamical simulations to compare circumplanetary disks formed by core accretion and disk instability, revealing significant differences in temperature and mass scaling that can help observationally distinguish the formation mechanisms.

Contribution

The paper provides a detailed comparison of circumplanetary disks from two formation scenarios, highlighting key temperature and mass differences through advanced simulations.

Findings

Circumplanetary disk mass scales linearly with protoplanetary disk mass.

Disks from gravitational instability are cooler (<100 K) compared to hotter core accretion disks (>1000 K).

Temperature differences can serve as observational criteria to identify formation mechanisms.

Abstract

Circumplanetary disks can be found around forming giant planets, regardless of whether core accretion or gravitational instability built the planet. We carried out state-of-the-art hydrodynamical simulations of the circumplanetary disks for both formation scenarios, using as similar initial conditions as possible to unveil possible intrinsic differences in the circumplanetary disk mass and temperature between the two formation mechanisms. We found that the circumplanetary disks mass linearly scales with the circumstellar disk mass. Therefore, in an equally massive protoplanetary disk, the circumplanetary disks formed in the disk instability model can be only a factor of eight more massive than their core-accretion counterparts. On the other hand, the bulk circumplanetary disk temperature differs by more than an order of magnitude between the two cases. The subdisks around planets formed by gravitational instability have a characteristic temperature below 100 K, while the core accretion circumplanetary disks are hot, with temperatures even greater than 1000 K when embedded in massive, optically thick protoplanetary disks. We explain how this difference can be understood as the natural result of the different formation mechanisms. We argue that the different temperatures should persist up to the point when a full-fledged gas giant forms via disk instability, hence our result provides a convenient criteria for observations to distinguish between the two main formation scenarios by measuring the bulk temperature in the planet vicinity.