The massive black hole at the Galactic Center

At the dynamic center of the Milky Way high spatial resolution, near-infrar ed 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* tin the constellation Sagittarius). Th ese measurements make a compelling case for the presence of a compact, cent ral dark mass of 2.6 x 10(6) solar masses. Simple physical considerations s how that this dark mass cannot consist of a stable cluster of stars, stella r remnants, substellar condensations or a degenerate gas of elementary part icles. Energy equipartition requires that at least 10(5) solar masses must be associated with SgrA* itself and is enclosed within less than 8 light mi nutes (equivalent to 15 Schwarzschild radii of a million solar mass black h ole). If one accepts these arguments it is hard to escape the conclusions t hat there must be a massive black hole at the core of the Milky Way.