Stellar Orbits around the Galactic Center Black Hole

We present new proper motion measurements and simultaneous orbital solutions for three newly identified (S0-16, S0-19, and S0-20) and five previously known (S0-1, S0-2, S0-3, S0-4, and S0-5) stars at the Galactic Center. This analysis pinpoints the Galaxy's central dark mass to within +-1 milli-arcsec and, for the first time from orbital dynamics, limits its proper motion to 0.8+-0.7 mas/y. The estimated central dark mass from orbital motions is (4.0+-0.3)x10^6(Ro/8kpc)^3 Mo; this is a more direct measure of mass than those obtained from velocity dispersion measurements, which are as much as a factor of two smaller. The smallest closest approach is achieved by S0-16, which confines the mass to within a radius…