The Galactic Center stellar cluster: The central arcsecond

Abstract

With 10 years of high-resolution imaging data now available on the stellar cluster in the Galactic Center, we analyze the dynamics of the stars at projected distances $\le 1.2^{\prime \prime }$ from the central black hole candidate Sagittarius A* (Sgr A*). We find evidence for radial anisotropy of the cluster of stars surrounding Sgr A*. We confirm/find accelerated motion for 6 stars, with 4 stars having passed the pericenter of their orbits during the observed time span. We calculated/constrained the orbital parameters of these stars. All orbits have moderate to high eccentricities. The center of acceleration coincides with the radio position of Sgr A*. From the orbit of the star S2, the currently most tightly constrained one, we determine the mass of Sgr A* to $3.3\pm 0.7\times 10^6$M${}_{\odot }$ and its position to $2.0\pm 2.4$ mas East and $2.7\pm 4.5$ mas South of the nominal radio position. The data provide compelling evidence that Sgr A* is a single supermassive black hole.

7 pages, 3 Figures; to be published in Astron. Nachr., Vol. 324, No. S1 (2003), Special Supplement "The central 300 parsecs of the Milky Way", Eds. A. Cotera, H. Falcke, T. R. Geballe, S. Markoff

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