Giant Planet Formation by Disk Instability in Low Mass Disks?

TL;DR

This study uses 3D radiative hydrodynamics simulations to evaluate the conditions under which disk instability can form giant planets, emphasizing the importance of disk mass and temperature in the process.

Contribution

The paper demonstrates that disk instability is less effective in low-mass disks and highlights the critical role of initial outer disk temperature in giant planet formation.

Findings

Disks with at least 0.043 solar masses can form self-gravitating clumps.

Higher outer disk temperatures reduce the likelihood of clump formation.

Low-mass disks around solar-mass stars rely on core accretion for giant planet formation.

Abstract

Forming giant planets by disk instability requires a gaseous disk that is massive enough to become gravitationally unstable and able to cool fast enough for self-gravitating clumps to form and survive. Models with simplified disk cooling have shown the critical importance of the ratio of the cooling to the orbital timescales. Uncertainties about the proper value of this ratio can be sidestepped by including radiative transfer. Three-dimensional radiative hydrodynamics models of a disk with a mass of $0.043 M_\odot$ from 4 to 20 AU in orbit around a $1 M_\odot$ protostar show that disk instabilities are considerably less successful in producing self-gravitating clumps than in a disk with twice this mass. The results are sensitive to the assumed initial outer disk ($T_o$) temperatures. Models with $T_o$ = 20 K are able to form a single self-gravitating clump, whereas models with $T_o$ = 25 K form clumps that are not quite self-gravitating. These models imply that disk instability requires a disk with a mass of at least $\sim 0.043 M_\odot$ inside 20 AU in order to form giant planets around solar-mass protostars with realistic disk cooling rates and outer disk temperatures. Lower mass disks around solar-mass protostars must rely upon core accretion to form inner giant planets.