The luminous S-star cluster in the Galactic center allows us to study the physics close to a super-massive black hole including distinctive dynamical tests of general relativity. Our best estimates for the mass of and the distance to Sgr A* is currently obtained using the three shortest period stars. Additionally, we aimed at a new and practical method to investigate the relativistic orbits of stars in the gravitational field near Sgr A*. From VLT single dish adaptive optics data we derive estimates of the orbital deformation due to relativistic effects. Accepting this result, S2 is the first star on a spatially resolved orbit around a super-massive black hole for which a post-Newtonian effect has been measured. In addition we studied the central regions of the Galactic Center to determine if the Circum-Nuclear Disk (CND) acts as an absorber or a barrier for the central X-rays diffuse emission surrounding the super massive black hole. 4.6 Ms of Chandra observations allow us to detect, for the first time, a shadow against the diffuse X-ray emission whose extent and location correspond to those of the CND. This information is used to derive characteristic properties of the X-ray emitting medium in the central few parsecs. We deduced that the CND rather acts as a barrier for the Galactic Center plasma and that the plasma located outside the CND may correspond to the collimated outflow possibly created by Sgr A* or the interaction between the wind of massive stars and the mini-spiral material.

22/02/2018 - 12:30
Prof. Andreas Eckart
I. Physikalisches Institut, Universitaet zu Koeln, Germany