Abstract
Evidence has been accumulating for several decades that quasars, the most luminous objects in the Universe, are powered by accretion of matter onto massive black holes. I will discuss recent observations, employing adaptive optics imaging and spectroscopy on large ground-based telescopes that prove the existence of such a massive black hole in the center of our Milky Way, beyond any reasonable doubt. These observations also indicate that the Galactic Center black hole may be rotating rapidly. The central black hole is surrounded by a cluster of young massive stars, partly arranged in two thin, rotating disks. I discuss possible explanations for this `paradox of youth'. I will also briefly discuss the cosmological evolution of massive black holes.