# Sustained FU Orionis-type outbursts from colliding discs in stellar flybys

**Authors:** Elisabeth M. A. Borchert, Daniel J. Price, Christophe Pinte, Nicolás Cuello  
**arXiv:** [2210.01143](https://arxiv.org/abs/2210.01143)  
**Date:** 2022-10-03  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2210.01143v1/

## Key points

- Study investigates effects of disc-disc stellar flybys on pre-existing circumstellar discs around both stars
- Flybys result in fast rising outbursts lasting 2-5 times longer than for a star-disc flyby when pre-existing circumstellar discs are present around both stars
- Perturber always goes into outburst with accretion rates exceeding $\dot{M}>10^{-5}~{\rm M_{\odot}~ yr^{-1}}$
- Primary goes into decades-long outburst only when the flyby is retrograde to the circumprimary disc rotation
- High accretion rates during the outburst are triggered by angular momentum cancellation in misaligned material generated by the encounter
- Large fraction of accreted material is alien to either star, which has important implications for our understanding of planet formation and evolution in binary systems.
- Sustained FU Orionis-type outbursts resulting from colliding discs in stellar flybys provide new insights into how binary interactions can shape the evolution of protoplanetary discs and influence planet formation processes.
- Importance of considering pre-existing circumstellar discs when studying binary interactions and their impact on disc evolution and planet formation processes is highlighted.

## Summary

In their recent study, Elisabeth M. A. Borchert and colleagues investigate the effects of disc-disc stellar flybys on pre-existing circumstellar discs around both stars using 3D hydrodynamics simulations with on-the-fly Monte Carlo radiative transfer. They find that such flybys result in fast rising outbursts lasting 2-5 times longer than for a star-disc flyby when pre-existing circumstellar discs are present around both stars. The perturber always goes into outburst, with accretion rates exceeding $\dot{M}>10^{-5}~{\rm M_{\odot}~ yr^{-1}}$. On the other hand, the primary goes into a decades-long outburst only when the flyby is retrograde to the circumprimary disc rotation. High accretion rates during the outburst are triggered by angular momentum cancellation in misaligned material generated by the encounter. The authors also note that a large fraction of accreted material is alien to either star, which has important implications for our understanding of planet formation and evolution in binary systems. These sustained FU Orionis-type outbursts resulting from colliding discs in stellar flybys provide new insights into how binary interactions can shape the evolution of protoplanetary discs and influence planet formation processes. Overall, this study highlights the importance of considering pre-existing circumstellar discs when studying binary interactions and their impact on disc evolution and planet formation processes. It demonstrates that disc collisions during stellar flybys can lead to long duration FU Orionis type outbursts due to angular momentum cancellation in misaligned material generated by encounters between two stars with pre-existing circumstellar discs. This has important implications for our understanding of planet formation and evolution in binary systems as a large fraction of accreted material is alien to either star involved in the interaction.