Polar alignment of a dusty circumbinary disc -- I. Dust ring formation

TL;DR

This study uses 3D simulations to show how dust traffic jams form dense rings in polar-aligning circumbinary discs, which could promote planet formation.

Contribution

It demonstrates the formation and longevity of dust rings during the polar alignment process in circumbinary discs, highlighting the role of dust-gas dynamics.

Findings

Dust rings form during disc misalignment and persist after polar alignment.

Dust rings drift inward with a timescale dependent on Stokes number.

Dust rings may facilitate streaming instability for planet formation.

Abstract

We investigate the formation of dust traffic jams in polar-aligning circumbinary discs. We use 3D smoothed particle hydrodynamical simulations of both gas and dust to model an initially highly misaligned circumbinary disc around an eccentric binary. As the circumbinary disc evolves to a polar configuration (perpendicular to the binary orbital plane), the difference in the precession between the gas and dust produces dust traffic jams, which become dense dust rings. We find the formation of dust rings exists for different Stokes number, binary eccentricity, and initial disc tilt. Dust rings are only produced while the circumbinary disc is misaligned to the binary orbital plane. When the disc becomes polar aligned, the dust rings are still present and long-lived. Once these dust rings are formed, they drift inward. The drift timescale depends on the Stokes number. The lower the Stokes number, the faster the dust ring drifts near the inner edge of the disc. The dust rings will have an increased midplane dust-to-go ratio, which may be a favourable environment for the steaming instability to operate.