Reinhard Genzel receives Karl Schwarzschild Medal 2011

July 13, 2011

The highest honour for astronomical research in Germany, the Karl Schwarzschild Medal of the German Astronomical Society (AG), this year goes to the Garching astrophysicist Reinhard Genzel, director at the Max Planck Institute for Extraterrestrial Physics. The AG bestows the award to a researcher who made a discovery with wide-reaching consequences. Genzel and teams were able to provide evidence that the centre of our Milky Way harbours a Black Hole. This Black Hole in the galactic centre is the best empirical evidence for the existence of these exotic objects that are postulated in Einstein's General Theory of Relativity.

Prof. Dr. Reinhard Genzel, winner of the Karl Schwarzschild Medal of the German Astronomical Society 2011

Black Holes are doubtless the most exotic objects in the Universe. Matter in a Black Hole is highly concentrated; it is compressed to such a high degree that even the speed of light is not fast enough to escape gravity. As neither radiation nor matter can move faster than the speed of light this leads to two consequences: light cannot escape a Black Hole, therefore it is invisible (hence the name). And matter falling into a Black Hole is gone forever. Nevertheless we know of the existence of Black Holes in space as their gravitational effects on their environments can be observed.

For some decades these kinds of observations have been obtained, but to find evidence for Black Holes was far from easy. For a long time astronomers suspected that the centres of so called "active galaxies" harbour Black Holes with several billion solar masses. Normal galaxies such as our Milky Way contain many hundred billion stars, planets, gas and dust. Active galaxies, such as quasars, in addition show extremely luminous nuclei and other strange phenomena, which can be well explained by a Black Hole in the centre swallowing matter. The observed effects, however, are only "indirect" evidence, since detailed measurements of these galaxies are very difficult because of the large distances involved.

Fig2: This image shows the close environment of the mysterious radio source Sgr A* in the centre of the Milky Way, where blue and red colours indicate images taken in the near and middle infrared obtained with the Very Large Telescope of the European Southern Observatory ESO in Chile, green is a radio image obtained with the Very Large Array of the US National Radio Astronomy Observatory. One of the stars, S2, is marked as well. The orbit of this star around the invisible centre could be followed for 19 years with extremely high accuracy (to the right of the image). From this motion the central mass can be deduced. Obviously S2 came very close to the central object in 2002. The very high orbital velocity of some 5000 km per second and the short distance to Sgr A* - only 17 light-hours - means that the enormous mass of 4.3 million solar masses has to be in a very small volume. The only physical explanation for this is a Black Hole.

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.

Other Interesting Articles

Go to Editor View