The Nuclear Cluster of the Milky Way: Star Formation and Velocity Dispersion in the Central 0.5 Parsec

Abstract

We report the first results of an extensive new study of the Galactic center stellar cluster. The central parsec is powered by a cluster of about two dozen luminous and helium-rich blue supergiants/Wolf-Rayet stars (T_eff ~ 20,000-30,000 K) with ZAMS masses up to ~100 M_☉. The most likely scenario for the formation of the massive stars is a small star formation burst between 3 × 10⁶ and 7 × 10⁶ years ago. In this scenario the Galactic center is presently in a short-lived, post-main-sequence "wind phase." In addition, there is evidence for another star formation event about 10⁸ years ago, as well as for recently formed massive stars that may have been transported into the central core along with orbiting gas streamers. The radial velocity dispersion of 35 early- and late-type stars with distances of 1''-12'' from Sgr A* is 154 ± 19 km s^-1. Our new results strongly favor the existence of a central dark mass of ~3 × 10⁶ M_☉ (density ≥ 10^8.5 M_☉ pc^-3, M/L ≥ 10 M_☉/L_☉) within 0.14 pc of the dynamic center.