The Nuclear Star CLuster and Central Massive Black Hole

Reinhard Genzel, Max Planck Institute for Extraterrestrial Physics

In the past decade high resolution measurements in the infrared employing adaptive optics imaging on 10m telescopes have allowed determining the three dimensional orbits stars within ten light hours of the compact radio source SgrA* at the Center of the Milky Way. These observations show that SgrA* is a three million solar mass black hole, beyond any reasonable doubt. The Galactic Center thus constitutes the best astrophysical evidence for the existence of black holes which have long been postulated, and is also an ideal 'lab' for studying the physics in the vicinity of such an object. Remarkably, young massive stars are present there and probably have formed in the innermost stellar cusp. Variable infrared and X-ray emission from SgrA* are a new probe of the physics and space time just outside the event horizon.