Origin of differences between low- and high-mass GI disks

Ascertain whether the observed differences between low disk-to-star mass ratio disks and high disk-to-star mass ratio disks in gravitational instability—particularly in the nature of spiral structure and transport—arise from fundamentally different dynamics, or whether both share the same dynamics with the typical perturbation scale and the deviation from local viscosity scaling with the disk scale height H.

Background

There is an apparent tension between modeling spiral substructures via global eigenmodes and modeling transport via a local viscosity prescription. Simulations suggest increasing global behavior with higher disk mass, but it is unclear whether this reflects different physics or a unified mechanism with different characteristic scales.

Clarifying this distinction is important for building consistent theoretical and observational models of gravitoturbulence and spiral structure across disk masses.

References

It is also unclear whether the difference between low-mass and high-mass disks are due to fundamental difference in the dynamics, or they share the same dynamics but with the typical scale of perturbation and the deviation from local viscosity proportional to the scale height H.

— Global Simulations of Gravitational Instability in Protostellar Disks with Full Radiation Transport. I. Stochastic Fragmentation with Optical-depth-dependent Rate and Universal Fragment Mass  (2410.12042 - Xu et al., 2024) in Section 1.2

Despite its astrophysical importance, this high-mass regime remains poorly understood in the context of protoplanetary discs. Early studies by have shown that for massive discs, the behaviour becomes more dynamical and is characterized by a series of recurrent phases of spiral activity. However, these studies were restricted to the simplest β cooling prescription and much remains to be understood in this context. Understanding what dynamical and observational imprints this early, globally unstable phase leaves on the subsequent disc structure and on the conditions for planet formation represents an open questions in the field.

— Gravitational instability in planet-forming discs  (2609.05080 - Longarini et al., 4 Sep 2026) in Section 5.1.1, Theoretical perspective, p. 19