arXiv subjects

Yannick Badoux

Publications and source records attributed to Yannick Badoux.

2 recordsLinked to original sources

arXiv2026

Planet-moon ejections in close stellar encounters

Free-floating planet-moon pairs (FFPMs) may form when planetary systems experience close stellar encounters. We quantify moon-retention probabilities and ejection cross sections for planets and planet-moon systems subject to close stellar encounters, and to dentify the orbital conditions most favorable for forming FFPMs. We conducted extensive numerical scattering experiments to compute ejection cross-sections on a grid in the orbital separation of the planet ($a_p$) and the moon ($a_m$), marginalizing over all other initial parameters. The simulations tracked both planetary and lunar fates across a wide range of encounter geometries. FFPM cross-sections depend on the moon semi-major axis $a_m$, decreasing gradually until a drop near $a_m\sim0.45\,R_H$. Planet-only ejection cross-sections instead decline steadily with $a_p$. Io-like moons ($a_m = 0.008\,R_H$) survive, but survival falls beyond $0.4\,R_H$. Compared with planet-planet scattering, stellar encounters preserve moons more effectively across all separations. Surviving moons at $a_m\lesssim 0.4\,R_H$ retain near-circular, low-inclination orbits, while wide-orbit moons show stronger dynamical excitation. Applying our cross-sections to the microlensing system MOA-2011-BLG-262Lb suggests possible progenitor semi-major axes between $a_p \sim 1.3$\,au and $\sim 5.9$ au for a solar-mass host. Uncertainties remain large and the probability distribution is flat but we prefer $a_p \sim 5.2$\,au. Stellar-encounter ejections constitute a viable channel for producing FFPMs whose orbital properties differ from those formed by planet-planet scattering. Moon retention and orbital excitation provide promising diagnostics of ejection history. Current and upcoming microlensing and direct-imaging surveys may be capable of detecting Galilean-mass moons around rogue planets, offering new tests of dynamical formation pathways.

astro-ph.EP↗

arXiv2026

Kozai-driven mass loss of the circumbinary disk in D9 in orbit around the supermassive black hole Sgr A*

The supermassive black hole (Sgr A*) in the Galactic center is surrounded by the S-star cluster consisting of young stars on eccentric orbits. Recently, the S-star binary, called D9, was found to be orbited by a circumbinary disk. Due to the gravitational interaction between Sgr A* and the binary, the disk could be short-lived. We investigate the evolution of the disk around a stellar binary while orbiting Sgr A*. We use the \texttt{AMUSE} framework for coupling a gravity solver (for the binary and Sgr. A*) with a hydrodynamics solver (for the disk). We find that, the disk eventually settles between 5.2$a_{\rm in}$ and 0.28 Hill radii of the binary. Here, $a_{\rm in}$ is the semi-major axis of D9. The inclination of the circumbinary disk follows the binary's, which evolves due to the von Zeipel-Lidov-Kozai (vZLK) mechanism induced by Sgr A*. The mean eccentricity of the disk is approximately in anti-phase with the eccentricity evolution of the binary. We find a vZLK timescale of $T_\text{vZLK}\approx62.5\,$kyr, which is two orders of magnitude shorter than the value reported by Peisker etal. (2024). As a consequence, D9 has undergone multiple vZLK oscillations in its lifetime of 2.7 Myr. We find the disk shows periodic bursts of mass loss on the vZLK timescale, suggesting that the mass loss itself is in part driven by the vZLK mechanism. The secular evolution observed in both the binary and the disk are consistent with theoretical predictions. We find the disk loses $\sim$7\% $\pm$ 2\% of its mass every vZLK cycle. If we extrapolate this mass loss, the disk will have 1\% of its current mass left after another $\sim$4 Myr. D9 will then be $\sim$6.7 Myr old, which is on the same order as the current average age of S cluster members. The vZLK-driven mass loss could, therefore, explain the absence of Br$\gamma$ emission from other S cluster members.

astro-ph.GA↗