Turbulent Dust-trapping Rings as Efficient Sites for Planetesimal Formation

TL;DR

This study demonstrates that turbulent dust-trapping rings in protoplanetary disks can efficiently concentrate dust to densities capable of gravitational collapse, providing a robust site for planetesimal formation even under turbulent conditions.

Contribution

The paper presents 3D non-ideal MHD simulations showing that dust-trapping rings in turbulent protoplanetary disks can lead to planetesimal formation, challenging previous theories based on streaming instability.

Findings

Strong dust clumping near pressure maxima

Dust densities exceed gravitational collapse threshold

Dust can concentrate in secondary filaments

Abstract

Recent observations of protoplanetary disks (PPDs) in the sub-mm have revealed the ubiquity of annular substructures, indicative of pebble-sized dust particles trapped in turbulent ring-like gas pressure bumps. This major paradigm shift also challenges the leading theory of planetesimal formation from such pebbles by the streaming instability, which operates in a pressure gradient and can be suppressed by turbulence. Here we conduct three-dimensional local shearing-box, non-ideal magnetohydrodynamic (MHD) simulations of dust trapping in enforced gas pressure bumps including dust backreaction. Under the moderate level of turbulence generated by the magnetorotational instability (MRI) with ambipolar diffusion that is suitable for outer disk conditions, we achieve quasi-steady states of dust trapping balanced by turbulent diffusion. We find strong dust clumping in all simulations near the gas pressure maxima, reaching a maximum density well above the threshold of triggering gravitational collapse to form planetesimals. A strong pressure bump concentrates dust particles towards bump center. With a weak pressure bump, dust can also concentrate in secondary filaments off the bump center due to dust backreaction, but strong clumping still occurs mainly in the primary ring around the bump center. Our results reveal dust-trapping rings as robust locations for planetesimal formation in outer PPDs, while they may possess diverse observational properties.