Properties and Evolution of the Central Stellar Cluster

Abstract

We discuss the implications of recent near-infrared imaging and spectroscopy of the Galactic Center stellar cluster. The central parsec appears to be powered by a cluster of hot, massive stars of which the IRS16 complex is the central core. In the 1 to 2µm band, the brightest members of this cluster are 10 to 15 HeI/HI emission line stars that can be characterized as ≈20,000 K, helium rich, very luminous supergiants. The HeI/HI stars can account for a major fraction of the total and Lyman continuum luminosity of the central parsec, but hotter, earlier type stars are probably required in addition to account for the He-continuum. The brightest cool stars in the central parsec are red supergiants, and asymptotic giant branch stars. We present two scenarios for the evolution of the central stellar core: one involves a small star formation burst a few 106 years ago that was the result of substantial prior gas influx into the core. In this scenario the Galactic Center is presently in a short-lived, post-main sequence “wind phase”. The second scenario involves the buildup of massive stars by sequential merging of lower mass stars. This scenario is plausible if the central stellar density significantly exceeds 107 M⊙ pc-3, as suggested by the surface density distribution on the near-infrared speckle maps. In this case massive star formation may proceed continuously.