The massive black hole at the galactic center

Abstract

At the dynamic center of the Milky Way high spatial resolution, near-infrared imaging and spectroscopy have made it possible in the last few years to measure stellar velocities down to separations of less than five light days from the compact radio source SgrA* (in the constellation Sagittarius). These measurements make a compelling case for the presence of a compact, central dark mass of 2.6 × 106 solar masses. Simple physical considerations show that this dark mass cannot consist of a stable cluster of stars, stellar remnants, substellar condensations or a degenerate gas of elementary particles. Energy equipartition requires that at least 105 solar masses must be associated with SgrA* itself and is enclosed within less than 8 light minutes (equivalent to 15 Schwarzschild radii of a million solar mass black hole). If one accepts these arguments it is hard to escape the conclusions that there must be a massive black hole at the core of the Milky Way.