Infrared Interferometry of the Galactic Center Black Hole

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 the GRAVITY infrared interferometry observations leading to the detection of the gravitational redshift and the Schwarzschild precession in the orbit of a star orbiting the black hole in a 16 yr orbit, and the observations of orbital motion of hot gas close to the innermost stable orbit. We further present the perspective for 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.