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Reinhard Genzel investigates the central mass of the Milky Way using the motion of nearby stars. He coauthored the 2002 report led by Rainer Schödel that followed a close stellar orbit around Sagittarius A*.

An orbital path tests more than a high stellar speed: its curvature, timing and closest approach constrain how tightly the attracting mass is concentrated. The measured short-period orbit required several million solar masses in a compact central region, providing strong dynamical evidence for a supermassive black hole.^[ref]