Feedback-limited Accretion: Variable Luminosity from Growing Planets

TL;DR

This study investigates how feedback from accreting giant planets influences their growth, gas dynamics, and observable variability, revealing that feedback reduces accretion rates and induces stochastic luminosity variations.

Contribution

The paper introduces a modified 2D simulation model incorporating planet feedback, demonstrating its effects on accretion variability and gas dynamics around giant planets.

Findings

Feedback reduces but does not stop accretion.

Accretion rate exhibits stochastic variability with ~10% amplitude.

Eccentric orbits produce periodic variability at half the orbital period.

Abstract

Planets form in discs of gas and dust around stars, and continue to grow by accretion of disc material while available. Massive planets clear a gap in their protoplanetary disc, but can still accrete gas through a circumplanetary disk. For high enough accretion rates the planet should be detectable at infrared wavelengths. As the energy of the gas accreted on to the planet is released, the planet surroundings heat up in a feedback process. We aim to test how this planet feedback affects the gas in the coorbital region and the accretion rate itself. We modified the 2D code FARGO-AD to include a prescription for the accretion and feedback luminosity of the planet and use it to model giant planets on 10 au circular and eccentric orbits around a solar mass star. We find that this feedback reduces but does not halt the accretion on to the planet, although this result might depend on the near-coincident radial ranges where both recipes are implemented. Our simulations also show that the planet heating gives the accretion rate a stochastic variability with an amplitude $\Delta \dot{M}_p \sim 0.1 \dot{M}_p$. A planet on an eccentric orbit ($e=0.1)$ presents a similar variability amplitude, but concentrated on a well-defined periodicity of half the orbital period and weaker broadband noise, potentially allowing observations to discriminate between both cases. Finally, we find that the heating of the coorbital region by the planet feedback alters the gas dynamics, reducing the difference between its orbital velocity and the Keplerian motion at the edge of the gap, which can have important consequences for the formation of dust rings.