Dominik Ostertag | Searcharxiv

arXiv2026

Substructures Induced by Dust Drag in Protoplanetary Disks

Dust substructures observed in protoplanetary disks are commonly attributed to embedded planets; however, intrinsic gas-dust interactions can also generate complex morphologies. We performed two-dimensional, axisymmetric simulations of gas and dust that include dust back-reaction and parameterized turbulence to investigate how the streaming instability (SI) and vertical shear instability (VSI) shape dust distributions. With moderate viscosity and sufficiently high metallicity, we identify a characteristic shuttlecock-shaped dust substructure composed of a dense, vertically settled "head" and a vertically extended "tail." This morphology arises from nonlinear SI driven by marginally coupled grains and the associated modification of gas flows. The dust scale height in the tail exceeds predictions based on the simple diffusion-settling balance, indicating strong self-generated turbulence. With lower viscosity, VSI becomes more vigorous, disrupts midplane structures, and increases vertical stirring; nevertheless, for dust grains with Stokes numbers around 0.01, SI can still attain dust-to-gas ratios of up to 20-50, potentially approaching the Hill density for gravitational binding. Our results demonstrate that intrinsic gas-dust interactions can generate prominent dust substructures even in disks with finite viscosity and, under favorable conditions, concentrate dust to levels relevant for planetesimal formation.

astro-ph.EP↗

arXiv2025

Strong clumping in global streaming instability simulations with a dusty fluid

Context: How planets form in protoplanetary disks and what drives the formation of their seeds is still a major unknown. It is an accepted theory that multiple processes can trap dusty material in radially narrow rings or vortex-like structures, preventing the dust from drifting inwards. However, the relevant process for clumping this dusty material until it collapses under gravity still needs to be identified. One promising candidate is the streaming instability arising from the aerodynamic interaction between dust and gas once they reach similar densities. Aims: We investigate with a global disk model based on recent observational constraints if streaming instability can form dust clumps, which might gravitationally collapse. Further, our goal is to verify the observability of the produced structures using ALMA or ngVLA. Methods. For the first time, we present global 2D (R, z) hydrodynamic simulations using FARGO3D in which the dust is treated as a pressureless fluid. The disk model assumes stratification, realistic boundary conditions, and meaningful resolution to resolve the fast-growing modes. We choose two values for the total dust-to-gas mass ratio Z = 0.01 and Z = 0.02, compare the maximum clump density to the local Hill density, and compute the optical depth of the dust disk. Results: With a dust-to-gas mass ratio of Z = 0.01, we confirm previous streaming instability simulations, not showing the ability to form strong concentrations of dust clumps. With Z = 0.02, dense clumps form within 20 orbits, however reaching only 30% of the Hill density even following disk parameters from the massive protoplanetary disks GM Aur, HD163296, IM Lup, MWC 480, and TW Hya, which all share astonishingly similar surface density profiles.

astro-ph.EP↗