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Session 97 - Galactic Structure, Galactic Center.
Oral session, Friday, January 09
Georgetown,
High spatial resolution, near-infrared imaging and spectroscopy of the nuclear star cluster obtained in the last few years have given key new insights about the mass distribution in the Milky Way Center. Measurements of radial and proper motions for more than 200 stars show that stellar velocities increase with a Kepler law down to a scale of a light week from the compact radio source Sgr A. The data make a compelling case for the presence of a compact, central dark mass of about 2.6\times10^6 M_ødot. Simple physical considerations show that this dark mass cannot consist of a stable cluster of stars, stellar remnants or substellar condensations. Energy equipartition requires that at least five percent of the dark mass (\ge10^5 M_ødot) must be associated with Sgr A^* itself and likely is enclosed within less than 8 light minutes. If one accepts these arguments it is hard to escape the conclusion that Sgr A^* is indeed a massive black hole at the core of the Milky Way.
