Some of my colleagues at the MPE IR group have been monitoring for more than 20 years the apparent position of the closest stars to the center of the Milky Way. From those observations they managed to reconstruct their stellar orbits and found that their foci coincide with a single point in the sky, with an estimated mass of the order of 4.3 million times the mass of the Sun. The density derived from this mass and the length of the closest stellar approach is so high that the only plausible explanation is that a supermassive black hole resides at the center of the Milky Way.
This sketch tries to simulate the movement of the stars around the Galactic Center black hole. The starting point uses the real deprojected stellar positions and velocities at a given moment in time kindly provided by Stefan Gillessen. The subsequent positions are calculated using Newton's law of universal gravitation and the leapfrog algorithm. The stellar colors and diameters are not real, as well as the black hole size and the optical effects that it produces.
The background image is a 70 micron continuum map of the central 2 arcminutes of the Milky Way obtained with the PACS photometer instrument on board of the Herschel satellite. The map was reduced using an automatic data processing pipeline that I have helped to develop as part of my work at MPE.
If the sketch doesn't work, you probably need to change your browser to one that supports WebGL.