Relativistic effects at the galactic center

Several stars orbit the - 3.67 x 10(6) M-circle dot black hole in the center of our Galaxy. Predictions had been made constraining the matter distribution about a central black hole, but it had been argued that predictions of General Relativistic (GR) effects, such as the apoastron shift of a star in close orbit, are limited by the possible existence of a compact stellar cluster (and/or a dark matter cusp) around the black bole. It was shown that current observations of the orbit of the S2 and S16 stars do allow us to constrain the parameter (mass and size) of the dark-matter cusp present in the center of the Galaxy. This work is reviewed here