The nature of the compact mass at the center of the Milky Way

The compact and very massive object located at the center of the Milky Way is currently the very best candidate for a super-massive black hole (SMBH) in our immediate vicinity. The outstanding importance of this phenomenon was underscored last year by the award of the Nobel Prize to three leading scientists in this field. I will summarize key results that led to this honor and highlight the Cologne contribution to it. The strongest evidence for the existence of a SMBH at the Galactic Center is provided by measurements of stellar orbits, variable X-ray emission, and strongly variable polarized near-infrared emission from the location of the radio source Sagittarius~A* (SgrA*) in the middle of the central stellar cluster. I will also explain the latest results obtained with the GRAVITY experiment on the Very Large Telescope Interferometer (VLTI). In the light of the experimental results one can also speculate on the charge and the black hole itself or the charge of orbiting source components.

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