The Complex Kinematics of the Young Stars Orbiting the Supermassive Black Hole in the Galactic Center Can Be Explained by the Presence of an Intermediate-mass Companion of Sgr A*

Abstract The subparsec proximity around the Sgr A ⋆ supermassive black hole (SMBH) in the center of the Milky Way contains an inner cluster of eccentric S-stars with randomly oriented orbits, a midway-disk of clockwise-rotating stars (CWSs), and a surrounding population of off-the-disk stars (ODSs). Despite their diverse kinematic properties, all three populations appear to be massive (WR/O/B types) and have similarly limited life span τ ⋆ ∼ 6–15 Myr. Several scenarios, including star formation induced by SMBH’s close encounters with one or more gas clouds as well as impulsive close scattering by a putative intermediate-mass companion (IMC) of Sgr A ⋆ possible an intermediate-mass black hole, have been proposed to explain the origin and dynamical evolution of S-stars, CWSs, ODSs, as well as hyper-velocity stars in the Galaxy. However, their coexistence and the origin of a recently discovered zone of avoidance in S-stars’ eccentricity-pericentric-distance distribution remain enigmatic. Here, we construct a unified model to comprehensively take into account these stars’ interaction with each other, their single natal disk, and an independent IMC. We show their disparate present-day orbits would only be concurrently attainable, within their multi-Myr age, under the combined influence of IMC’s secular perturbation and these stars’ resonant relaxation in a depleting gaseous-disk environment.