By doing a largely automatized re-analysis of all the imaging data, we were able to increase the number of measured proper motions in the Galactic Center stellar cluster by about an order of magnitude in comparison to previous work done on this issue. We thus have made astrometric positions and projected sky velocities available for about 1000 stars in the central parsec of our galaxy. We are now able to assess the dynamical properties of the central stellar cluster with unprecedented accuracy and completeness.

Our results find significant orbital curvature (acceleration) for two stars, S1 and S2, very close to the black hole candidate Sgr A* (see Figure). Their acceleration vectors point towards the location of this dark point-like mass and allow estimating its magnitude, which lies between 2.6 to 3.3 million solar masses. Several arcseconds away from Sgr A* we found a number of interesting high velocity stars (projected velocity approximately 500 km/s), that seem to be witnesses of the unusually strong interactions between the stars in this very dense cluster.

The new and extensive data on precise positions and velocities of Galactic Center cluster stars will also facilitate further analysis, like the search for pairs of images of stars that are being gravitationally lensed by the central dark mass. New data, as they are expected from observations with CONICA on the VLT in this and the following years, can be readily added to our data basis.

The central region (~0.5 light years) of the Milky Way. Two inset blow-ups show the central cluster in two epochs (1994, 2000). Obviously, the distribution of stars in this region has changed dramatically over less than a decade. The proper motions of the two stars showing acceleration are shown as an overlay. Fast moving stars also exist outside the immediate vicinity of Sgr A*. One of these stars is marked in the image with an arrow indicating its direction of motion. All images were acquired with the infrared speckle camera SHARP (built at MPE) on the ESO telescope NTT in Chile.