Gravitational Instabilities in Gaseous Protoplanetary Disks and Implications for Giant Planet Formation

TL;DR

This paper reviews how gravitational instabilities in protoplanetary disks can lead to giant planet formation, discussing numerical models, physical processes, and observational constraints.

Contribution

It provides a comprehensive overview of disk instability mechanisms and recent multi-code simulation results, advancing understanding of giant planet formation pathways.

Findings

Gravitational instabilities can produce spiral arms and dense clumps in protoplanetary disks.

Disk cooling rates influence whether self-gravitating clumps form.

Hybrid scenarios may facilitate planet formation via both GI and core accretion.

Abstract

Protoplanetary gas disks are likely to experience gravitational instabilites (GI's) during some phase of their evolution. Density perturbations in an unstable disk grow on a dynamic time scale into spiral arms that produce efficient outward transfer of angular momentum and inward transfer of mass through gravitational torques. In a cool disk with rapid enough cooling, the spiral arms in an unstable disk form self-gravitating clumps. Whether gas giant protoplanets can form by such a disk instability process is the primary question addressed by this review. We discuss the wide range of calculations undertaken by ourselves and others using various numerical techniques, and we report preliminary results from a large multi-code collaboration. Additional topics include -- triggering mechanisms for GI's, disk heating and cooling, orbital survival of dense clumps, interactions of solids with GI-driven waves and shocks, and hybrid scenarios where GI's facilitate core accretion. The review ends with a discussion of how well disk instability and core accretion fare in meeting observational constraints.