Experimental Indicators of Accretion Processes in Active Galactic Nuclei

Bright Active Galactic Nuclei are powered by accretion of mass onto thesuper massive black holes at the centers of the host galaxies.For fainter objects star formation may significantly contribute to the luminosity.We summarizeexperimental indicators of the accretion processes in Active Galactic Nuclei (AGN), i.e.,observable activity indicators that allow us to conclude on the nature of accretion.The Galactic Center is the closest galactic nucleus that can be studied with unprecedentedangular resolution and sensitivity.Therefore, here we also include the presentation of recent observational results on Sagittarius~A*and the conditions for star formation in the central stellar cluster.We cover results across the electromagnetic spectrumand find that the Sagittarius~A* (SgrA*) systemis well ordered with respect to its geometrical orientation and itsemission processes of which we assume to reflect theaccretion process onto the super massive black hole.