On the origin of kinematic distribution of the sub-parsec young stars in the Galactic center

TL;DR

This paper proposes that the diverse kinematic distribution of young stars near the Galactic center results from a past perturbation by an intermediate-mass black hole or dark cluster, which dynamically influenced the stellar disk.

Contribution

It introduces a hypothesis that a migrating intruder perturbed a young stellar disk, explaining the observed dynamical dichotomy in the Galactic center's stellar population.

Findings

Perturbation by an IMBH or dark cluster can produce the observed eccentricities and inclinations.

Stars in the inner disk remain coplanar, while outer stars are dynamically excited.

Future kinematic measurements can test this hypothesis and reveal hidden massive objects.

Abstract

Within a half-parsec from the Galactic center (GC), there is a population of coeval young stars which appear to reside in a coherent disk. Surrounding this dynamically-cool stellar system, there is a population of stars with a similar age and much larger eccentricities and inclinations relative to the disk. We propose a hypothesis for the origin of this dynamical dichotomy. Without specifying any specific mechanism, we consider the possibility that both stellar populations were formed within a disk some 6 Myr ago. But this orderly structure was dynamically perturbed outside-in by an intruding object with a mass ~10^4 Msun, which may be an intermediate-mass black hole (IMBH) or a dark stellar cluster hosting an IMBH. We suggest that the perturber migrated inward to ~0.15-0.3pc from the GC under the action of dynamical friction. Along the way, it captured many stars in the outer disk region into its mean-motion resonance, forced them to migrate with it, closely encountered with them, and induced the growth of their eccentricity and inclination. But stars in the inner regions of the disk retain their initial coplanar structure. We predict that some of the inclined and eccentric stars surrounding the disk may have similar Galactocentric semimajor axis. Future precision determination of their kinematic distribution of these stars will not only provide a test for this hypothesis but also evidences for the presence of an IMBH or a dark cluster at the immediate proximity of the massive black hole at the GC. (abridged)