Latest News from the Galactic Center

Located at 8kpc distance only, SgrA* is the closest supermassive black hole. Due to its proximity it can be observed in unparalleled detail, making the Galactic Center a unique astrophysical laboratory. Our team has been tracking the motions of individual stars on their orbits around SgrA* for more than 25 years. These observations show that SgrA* is a black hole beyond reasonable doubt and measure its mass and distance with percent-level accuracy. Recently, our team has put into operation the near-infrared interferometer 'GRAVITY' at ESO's VLT in Chile. Compared to previous, adaptive optics based data, GRAVITY delivers 15 x sharper images and has increased our astrometric precision by a similar factor. Here, we report on the scientific progress achieved with this new tool: In 2018, the star S2 has passed the pericenter of its 16-year orbit, reaching a velocity of almost 8000 km/s. The fly-by was close enough to detect the gravitational redshift of the stellar light in the gravitational field of SgrA*, and we have obtained a highly significant detection of the redshift signal because of the extremely precise, GRAVITY-based orbit determination. Further, we have observed with GRAVITY the emission of SgrA* itself, and we have found that during three flares the emission is not stationary, but rotates clockwise with a radius a few times the gravitational radius and a period of around 45 minutes. Our data show that we see the SgrA* system nearly face-on. In 2019, we aim at measuring the Schwarzschild precession of S2 as it moves away from SgrA*.