Ring Formation in Protoplanetary Disks Driven by an Eccentric Instability

TL;DR

This paper demonstrates that protoplanetary disks can spontaneously form multiple concentric rings due to an eccentric cooling instability, without the need for embedded planets, supported by theory and hydrodynamics simulations.

Contribution

It introduces a new mechanism for ring formation in disks driven by an eccentric instability, validated through linear theory and non-linear simulations.

Findings

Multiple long-lived rings can form spontaneously in disks.

The instability mechanism aligns with observed disk features.

Eccentric motions in rings may be detectable observationally.

Abstract

We find that, under certain conditions, protoplanetary disks may spontaneously generate multiple, concentric gas rings without an embedded planet through an eccentric cooling instability. Using both linear theory and non-linear hydrodynamics simulations, we show that a variety of background states may trap a slowly precessing, one-armed spiral mode that becomes unstable when a gravitationally-stable disk rapidly cools. The angular momentum required to excite this spiral comes at the expense of non-uniform mass transport that generically results in multiple rings. For example, one long-term hydrodynamics simulation exhibits four long-lived, axisymmetric gas rings. We verify the instability evolution and ring formation mechanism from first principles with our linear theory, which shows remarkable agreement with the simulation results. Dust trapped in these rings may produce observable features consistent with observed disks. Additionally, direct detection of the eccentric gas motions may be possible when the instability saturates, and any residual eccentricity leftover in the rings at later times may also provide direct observational evidence of this mechanism.