The nuclear star cluster of the Milky Way

Schödel, Rainer; Merritt, David; Eckart, Andreas
"Journal of Physics: Conference Series, Volume 131, Proceedings of "The Universe Under the Microscope - Astrophysics at High Angular Resolution", held 21-25 April 2008, in Bad Honnef, Germany. Editors: Rainer Schoedel, Andreas Eckart, Susanne Pfalzner and Eduardo Ros, pp. 012044 (2008)."


The nuclear star cluster of the Milky Way is a unique target in the Universe. Contrary to extragalactic nuclear star clusters, using current technology it can be resolved into tens of thousands of individual stars. This allows us to study in detail its spatial and velocity structure as well as the different stellar populations that make up the cluster. Moreover, the Milky Way is one of the very few cases where we have firm evidence for the co-existence of a nuclear star cluster with a central supermassive black hole, Sagittarius A*. The number density of stars in the Galactic center nuclear star cluster can be well described, at distances gtrsim 1 pc from Sagittarius A*, by a power-law of the form p(r) ∞ r with an index of γ thickapprox 1.8. In the central parsec the index of the power-law becomes much flatter and decreases to γ thickapprox 1.2. We present proper motions for more than 6000 stars within 1 pc in projection from the central black hole. The cluster appears isotropic at projected distances gtrsim 0.5 pc from Sagittarius A*. Outside of 0.5 pc and out to 1.0 pc the velocity dispersion appears to stay constant. A robust result of our Jeans modeling of the data is the required presence of 0.5 — 2.0 x 106 Modot of extended (stellar) mass in the central parsec of the Galaxy.