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

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 13CO 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 α-viscosity of α = 0.038 ± 0.018. This value implies an accretion rate onto the central star of log10 Ṁ⋆ = −6.99 ± 0.17 M⊙ yr−1, which reproduces the one observed value of log10 Ṁ⋆,obs = −7.2 ± 0.5 M⊙ yr−1 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.