Angular momentum transport via gravitational instability in the Elias 2-27 disc

TL;DR

This study uses ALMA observations to quantify how gravitational instability drives angular momentum transport in the Elias 2-27 protoplanetary disc, confirming its dominant role through measured accretion rates.

Contribution

It provides the first direct measurement of angular momentum transport efficiency via gravitational instability in Elias 2-27 using observed kinematic signatures.

Findings

Measured alpha-viscosity of 0.038±0.018 indicating efficient angular momentum transport.

Calculated accretion rate matches observed values within uncertainties.

Confirmed gravitational instability as the primary mechanism for angular momentum transport in this system.

Abstract

Gravitational instability is thought to be one of the main drivers of angular momentum transport in young protoplanetary discs. The disc around Elias 2-27 offers a unique example of gravitational instability at work. It is young and massive, displaying two prominent spiral arms in dust continuum emission and global non-axisymmetric kinematic signatures in molecular line data. In this work, we used archival ALMA observations of $^{13}$CO line emission to measure the efficiency of angular momentum transport in the Elias 2-27 system through the kinematic signatures generated by gravitational instability, known as 'GI wiggles'. Assuming the angular momentum is transported by the observed spiral structure and leveraging previously-derived dynamical disc mass measurements, the amount of angular momentum transport we found corresponds to an $\alpha-$viscosity of $\alpha=0.038\pm0.018$. This value implies an accretion rate onto the central star of $\log_{10}\dot{M}_\star=-6.99\pm0.17\text{M}_\odot/\text{yr, which}$ reproduces the one observed value of $\log_{10}\dot{M}_{\star,\text{obs}}=-7.2\pm0.5\text{M}_\odot/\text{yr }$ very well. The excellent agreement we have found serves as further proof that gravitational instability is the main driver of angular momentum transport acting in this system.