On the rise times in FU Orionis events

TL;DR

This study uses 3D hydrodynamics and radiative transfer simulations to show that stellar flybys can trigger FU Orionis outbursts with characteristic rise times and accretion rates, matching observations.

Contribution

It demonstrates that stellar flybys can initiate FU Orionis outbursts and explains the observed accretion dynamics and dominant star behavior.

Findings

Flybys trigger 1-2 year rise in accretion rate to 10^{-4} M_sun/yr

High accretion rates persist for over a hundred years

The less massive star becomes the dominant accretor during outbursts

Abstract

We examine whether stellar flyby simulations can initiate FU Orionis outbursts using 3D hydrodynamics simulations coupled to live Monte Carlo radiative transfer. We find that a flyby where the secondary penetrates the circumprimary disc triggers a 1-2 year rise in the mass accretion rate to $10^{-4}~{\rm M_{\odot}~ yr^{-1}}$ that remains high ($\gtrsim 10^{-5}~{\rm M_{\odot}~yr^{-1}}$) for more than a hundred years, similar to the outburst observed in FU Ori. Importantly, we find that the less massive star becomes the dominant accretor, as observed.