The influence of dense gas rings on the dynamics of a stellar disk in the Galactic center

TL;DR

This study uses simulations to examine how dense gas rings influence the dynamics of stellar disks near the Galactic center, revealing that inner rings can significantly alter stellar orbits over a few million years.

Contribution

It demonstrates through combined N-body and hydrodynamics simulations that inner gas rings can induce precession and dismemberment of stellar disks, a novel insight into Galactic center dynamics.

Findings

Inner gas rings induce significant precession of stellar orbits.

Outer circumnuclear rings are ineffective in affecting stellar disks within 3 Myr.

Precession effects are stronger when the stellar disk and gas ring are coplanar.

Abstract

The Galactic center hosts several hundred early-type stars, about 20% of which lie in the so-called clockwise disk, while the remaining 80% do not belong to any disks. The circumnuclear ring (CNR), a ring of molecular gas that orbits the supermassive black hole (SMBH) with a radius of 1.5 pc, has been claimed to induce precession and Kozai-Lidov oscillations onto the orbits of stars in the innermost parsec. We investigate the perturbations exerted by a gas ring on a nearly-Keplerian stellar disk orbiting a SMBH by means of combined direct N-body and smoothed particle hydrodynamics simulations. We simulate the formation of gas rings through the infall and disruption of a molecular gas cloud, adopting different inclinations between the infalling gas cloud and the stellar disk. We find that a CNR-like ring is not efficient in affecting the stellar disk on a timescale of 3 Myr. In contrast, a gas ring in the innermost 0.5 pc induces precession of the longitude of the ascending node Omega, significantly affecting the stellar disk inclination. Furthermore, the combined effect of two-body relaxation and Omega-precession drives the stellar disk dismembering, displacing the stars from the disk. The impact of precession on the star orbits is stronger when the stellar disk and the inner gas ring are nearly coplanar. We speculate that the warm gas in the inner cavity might have played a major role in the evolution of the clockwise disk.