2025MNRAS.543.1798P

Stellar flybys are likely to be common in young star-forming regions and could be responsible for substructures observed in protoplanetary discs. Using 3D smoothed particle hydrodynamics simulations, we study dust trapping in discs perturbed by parabolic coplanar flybys. We find that spiral structures are induced in the gas and dust discs for both prograde and retrograde encounters. By tracking individual dust particles within the flyby-induced substructures, we determine that they have a highly enhanced dust-to-gas ratio compared to particles in an unperturbed disc. We further find that the local dust-to-gas ratios in flyby-induced substructures are sufficiently high to trigger the streaming instability and hence facilitate planetesimal formation in young discs.