The Nuclear Star Cluster of the Milky Way: Star Formation, Dynamics and Central Black Hole

Reinhard Genzel

Max-Planck-Institut für extraterrestrische Physik, Garching, FRG, and Department of Physics, University of California at Berkeley, USA

Paper: To appear in the Proceedings of the Star2000 Meeting (Heidelberg, March 2000), editor R. Spurzem

EPrint Server: astro-ph/0008119


Abstract:

High spatial resolution, near-infrared imaging and spectroscopy of the nuclear star cluster have given key new insights about the dynamics, evolution and mass distribution in the Milky Way Center. The central parsec is powered by a cluster of hot, massive stars which must have formed a few million years ago. Either star formation was triggered in the central parsec by the infall of a very dense cloud, or a dense, young star cluster formed outside of the central parsec sank rapidly into the nuclear region through dynamical friction. The presence of luminous asymptotic giant branch (AGB) stars suggests that there were earlier such star formation episodes. Measurements of radial and proper motions for more than 200 stars delineate the stellar dynamics to a scale of a few light days from the dynamic center which is coincident with the compact radio source (Sgr A^*) within 0.1'' (800 AU). The stellar velocities increase toward Sgr A^* with a Kepler law (to >1000 km/s for the innermost stars), implying the presence of a three million solar mass central (dark) mass. The observations make a compelling case that this mass concentration is a black hole which is currently accreting at a low rate or radiating at low efficiency. With the exception of the young, massive stars the velocity field of the central stellar cluster is close to isotropic. The young stars are characterized by a turbulent rotation pattern that still carries the imprint of the angular momentum distribution in the original cloud or star cluster.


Preprints available from the authors at genzel@mpe.mpg.de , or the raw TeX (no figures) if you click here.

Back to the gcnews home-page.