Anatomy of a Fall: Stationary and super-Keplerian spiral arms generated by accretion streamers in protostellar discs

TL;DR

This study uses 3D simulations to explore how accretion streamers induce diverse, long-lived spiral arms in protoplanetary discs, revealing their potential observational signatures and similarities to companion-induced spirals.

Contribution

It demonstrates that streamer-disc interactions can generate stationary and super-Keplerian spiral arms with varied pattern speeds, lasting much longer than the initial infall, a novel insight into disc substructure formation.

Findings

Streamers excite long-lived spiral arms with various pattern speeds.

Spiral arms can have large, sudden pitch angle changes.

Induced spirals resemble those caused by massive companions.

Abstract

Late-stage infall onto evolved protoplanetary discs is an important source of material and angular momentum replenishment, and disc substructures. In this paper we used 3D smoothed particle hydrodynamics simulations to model streamer-disc interactions for a prograde streamer. The initially parabolic streamer interacts with the disc material to excite disc eccentricity, which can last on the order of $10^5$ years. We found that the spiral arms the streamer excited in the disc can have a variety of pattern speeds, ranging from stationary to super-Keplerian. Spiral arms with various pattern speeds can exist simultaneously, providing a way to diagnose them in observations. Streamer induced spirals appear similar to those generated by a massive outer companion, where the pitch angle of the spiral increases towards the source of the perturbation. Additionally, the spirals arms can show large and sudden pitch angle changes. Streamer induced spirals are long-lived, lasting approximately $3-4\times$ longer than the initial streamer infall timescale ($\sim$$10^4$ years). After the initial interaction with the disc, a long lasting low $m$ azimuthal mode persists in the disc.