2024A&A...686L...6L

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 log₁₀Ṁ_⋆ = -6.99 ± 0.17 M_⊙ yr^–1, which reproduces the one observed value of log₁₀Ṁ_⋆,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.