Kinematic Structure of the Galactic Center S-cluster

TL;DR

This paper analyzes the kinematics of 112 stars in the Galactic Center's S-cluster, revealing two nearly edge-on disks with opposite rotation directions, possibly formed by resonance or influenced by a nearby disturber.

Contribution

It provides the first detailed kinematic analysis of the S-cluster stars, uncovering their disk-like structure and rotation patterns near the supermassive black hole.

Findings

Stars are arranged in two nearly edge-on disks.

Disks have opposite rotation directions.

Disk poles are close to the line of sight.

Abstract

We present a detailed analysis of the kinematics of 112 stars that mostly comprise the high velocity S-cluster and orbit the super massive black hole SgrA* at the center of the Milky Way. For 39 of them orbital elements are known, for the remainder we know proper motions. The distribution of inclinations, and proper motion flight directions deviate significantly from a uniform distribution which one expects if the orientation of the orbits are random. Across the central arcseconds the S-cluster stars are arranged in two almost edge on disks that are located at a position angle approximately +-45 o with respect to the Galactic plane. The angular momentum vectors for stars in each disk point in both directions, i.e. the stars in a given disk rotate in opposite ways. The poles of this structure are located only about 25 o from the line of sight. This structure may be the result of a resonance process that started with the formation of the young B-dwarf stars in the cluster about 6 Myr ago. Alternatively, it indicated the presence of a disturber at a distance from the center comparable to the distance of the compact stellar association IRS13.