# Flybys in protoplanetary discs: I. Gas and dust dynamics

## TL;DR

This study uses 3D simulations to analyze how stellar flybys affect protoplanetary discs, revealing long-lasting spiral structures, dust-gas differences, and potential outbursts, with implications for disc evolution.

## Contribution

It provides the first detailed 3D modeling of gas and dust dynamics during inclined stellar flybys, highlighting their lasting impact on disc structure and activity.

## Key findings

- Flybys induce long-lived spiral structures in gas and dust.
- Dust and gas structures differ due to drag effects on dust grains.
- Flybys can cause accretion rate variations and FU Orionis-like outbursts.

## Abstract

We present 3D smoothed particle hydrodynamics simulations of protoplanetary discs undergoing a flyby by a stellar perturber on a parabolic orbit lying in a plane inclined relative to the disc mid-plane. We model the disc as a mixture of gas and dust, with grains ranging from 1 {\mu}m to 10 cm in size. Exploring different orbital inclinations, periastron distances and mass ratios, we investigate the disc dynamical response during and after the flyby. We find that flybys induce evolving spiral structure in both gas and dust which can persist for thousands of years after periastron. Gas and dust structures induced by the flyby differ because of drag-induced effects on the dust grains. Variations in the accretion rate by up to an order of magnitude occur over a time-scale of order 10 years or less, inducing FU Orionis-like outbursts. The remnant discs are truncated and warped. The dust disc is left more compact than the gas disc, both because of disc truncation and accelerated radial drift of grains induced by the flyby.