Is the spiral morphology of the Elias 2-27 circumstellar disc due to gravitational instability?

TL;DR

This study investigates whether the spiral arms in the Elias 2-27 disc are caused by gravitational instability, finding that specific conditions are required, but alternative explanations might be more plausible.

Contribution

The paper demonstrates that observable spiral structures due to self-gravity require very specific disc conditions, challenging the assumption that gravity alone explains the Elias 2-27 morphology.

Findings

Observable spirals from self-gravity need low opacity and minimal external irradiation.

The parameter space for self-gravity explanation is very narrow.

External perturbations may better explain the observed structure.

Abstract

A recent ALMA observation of the Elias 2-27 system revealed a two-armed structure extending out to ~300 au in radius. The protostellar disc surrounding the central star is unusually massive, raising the possibility that the system is gravitationally unstable. Recent work has shown that the observed morphology of the system can be explained by disc self-gravity, so we examine the physical properties of the disc necessary to detect self-gravitating spiral waves. Using three-dimensional Smoothed Particle Hydrodynamics, coupled with radiative transfer and synthetic ALMA imaging, we find that observable spiral structure can only be explained by self-gravity if the disc has a low opacity (and therefore efficient cooling), and is minimally supported by external irradiation. This corresponds to a very narrow region of parameter space, suggesting that, although it is possible for the spiral structure to be due to disc self-gravity, other explanations, such as an external perturbation, may be preferred.