In comparison to these galaxies, the centre of our own Milky Way is very close, only about 25000 light-years away. Could such a "gravity monster" lurk there as well? To solve this riddle, Reinhard Genzel and his team observed the motions of stars in the vicinity of the mysterious radio source Sgr A* in the centre of our galaxy with high accuracy. Their idea: From the movement of celestial objects around a central body its mass can be determined. And indeed, the stars in the centre of the Milky Way are orbiting an invisible "something", and they are orbiting fast. More than twenty years of observation led to only one conclusion: our galaxy harbours a Black Hole with 4.3 million solar masses! (See Fig. 2 and the image caption for details.) We now think that these central Black Holes exist in almost all galaxies. Unlike active galaxies, however, most of them do not attract attention as they are "starving", i.e. they do not feed on matter from their surroundings.
The AG honours Reinhard Genzel not only for this discovery, but rather for all his activities in observational astronomy. These include his important contributions to the development of new observing techniques and instruments in Infrared and Submillimetre astronomy, which operate at today's large observatories, such as those of the European Southern Observatory. Only these techniques made it possible to carry out the highly precise measurements in the centre of our galaxy.