Predicting the kinematic evidence of gravitational instability

TL;DR

This paper predicts observable kinematic signatures of gravitational instability in protoplanetary discs, which can be detected via molecular line observations, helping to confirm disc masses and the role of instability in planet formation.

Contribution

It introduces hydrodynamics simulations with radiative transfer to identify kinematic evidence of gravitational instability in protoplanetary discs, a novel approach for direct detection.

Findings

Kinematic signatures are independent of viewing angle.

Simulations show clear signatures of gravitational instability.

Detection can confirm disc mass and instability presence.

Abstract

Observations with the Atacama Large Millimeter/Submillimeter array (ALMA) have dramatically improved our understanding of the site of exoplanet formation: protoplanetary discs. However, many basic properties of these discs are not well-understood. The most fundamental of these is the total disc mass, which sets the mass budget for planet formation. Discs with sufficiently high masses can excite gravitational instability and drive spiral arms that are detectable with ALMA . Although spirals have been detected in ALMA observations of the dust , their association with gravitational instability, and high disc masses, is far from clear. Here we report a prediction for kinematic evidence of gravitational instability. Using hydrodynamics simulations coupled with radiative transfer calculations, we show that a disc undergoing such instability has clear kinematic signatures in molecular line observations across the entire disc azimuth and radius which are independent of viewing angle. If these signatures are detected, it will provide the clearest evidence for the occurrence of gravitational instability in planet-forming discs, and provide a crucial way to measure disc masses.