Clockwise Stellar Disk and the Dark Mass in the Galactic Center

Abstract

Two disks of young stars have recently been discovered in the Galactic center. The disks are rotating in the gravitational field of the central black hole at radii r ~ 0.1-0.3 pc and thus open a new opportunity to measure the central mass. We find that the observed motion of stars in the clockwise disk implies the mass within -0.1 pc M = (4.3 ± 0.5) × 106 M☉ for the fiducial distance to the Galactic center R0 = 8 kpc, and we derive the scaling of M with R0. As a tool for our estimate we use orbital roulette, a recently developed method. The method reconstructs the three-dimensional orbits of the disk stars and checks the randomness of their orbital phases. We also estimate the three-dimensional positions and orbital eccentricities of the clockwise-disk stars.