Generation of highly inclined protoplanetary discs through single stellar flybys

TL;DR

This study investigates how single stellar flybys can induce significant inclinations in protoplanetary discs, potentially explaining the formation of misaligned planets, through detailed hydrodynamic simulations of various orbital configurations.

Contribution

It demonstrates that stellar flybys, especially retrograde orbits, can produce disc inclinations up to 60°, offering a plausible mechanism for misaligned planet formation.

Findings

Retrograde flybys generate inclinations up to 60°

Prograde flybys cause significant disc mass loss

Flybys can explain misaligned Hot Jupiters up to 60°

Abstract

We study the three-dimensional evolution of a viscous protoplanetary disc which is perturbed by a passing star on a parabolic orbit. The aim is to test whether a single stellar flyby is capable to excite significant disc inclinations which would favour the formation of so-called misaligned planets. We use smoothed particle hydrodynamics to study inclination, disc mass and angular momentum changes of the disc for passing stars with different masses. We explore different orbital configurations for the perturber's orbit to find the parameter spaces which allow significant disc inclination generation. Prograde inclined parabolic orbits are most destructive leading to significant disc mass and angular momentum loss. In the remaining disc, the final disc inclination is only below $20^\circ$. This is due to the removal of disc particles which have experienced the strongest perturbing effects. Retrograde inclined parabolic orbits are less destructive and can generate disc inclinations up to $60^\circ$. The final disc orientation is determined by the precession of the disc angular momentum vector about the perturber's orbital angular momentum vector and by disc orbital inclination changes. We propose a sequence of stellar flybys for the generation of misalignment angles above $60^\circ$. The results taken together show that stellar flybys are promising and realistic for the explanation of misaligned Hot Jupiters with misalignment angles up to 60\degr.