Speaker
Description
The Galactic Center harbors the nearest massive black hole. With a distance of only 8 kpc, it is the closest laboratory to study the astrophysical processes at work in these extreme objects, and to probe Einstein's general theory of relativity in the regime of strong gravity. Our presentation gives an overview of adaptive optics and GRAVITY infrared interferometry observations of stellar orbits, the detection of the gravitational redshift and the Schwarzschild precession in the orbit of a star, and the observations of orbital motion of hot gas close to the innermost stable orbit. So far all observations are fully described by the laws of general relativity and the motion around a single black hole. We give upper limits on the deviation from general relativity, the extended mass, and the mass of potential intermediate mass black holes. The observed motion and polarization loops during a flare are explained by a magnetically dominated accretion and suggest that the accretion flow is fueled by the winds of nearby, young, massive stars. We end our presentation with an outlook on future measurements of the spin and quadrupole of the black hole by combining infrared interferometry and spectroscopy form extremely large telescopes, which will then also test the cosmic censorship and no hair theorem of black holes.
