Reinhard Genzel

2003 Balzan Prize for Infrared Astronomy

Professor Reinhard Genzel has made fundamental contributions to infrared astronomy. He has developed instrumentation which enabled him and colleagues to make outstanding discoveries, including evidence for a massive black hole in the centre of our galaxy.

Infrared light falls outside the range of radiation that can be perceived by the human eye. Nevertheless, infrared radiation reaches the Earth from most astronomical objects in the Universe, and efficient devices have been developed to detect this infrared radiation.
A significant advantage of infrared as well as radio radiation is that it penetrates dust dispersed in interstellar space much more easily than optically perceived radiation. Thus, it is possible to see through the dense dust clouds surrounding places where stars are born, and to reach the interesting region around the centre of our galaxy, which is hidden behind vast regions of dust. Infrared radiation also lends itself to the technique of adaptive optics, which corrects the blurring of the image by the Earth’s atmosphere through the use of a rapidly deformable mirror in the ray path.

Reinhard Genzel is an experimental scientist who has designed, built, and used innovative infrared equipment on ground telescopes, in high flying aircraft, and in space craft. Reinhard Genzel and his group have contributed some of the most important and innovative instruments to the Very Large Telescope of the European Southern Observatory in Chile, like the spectrograph SINFONI, combined with laser beam assisted adaptive optics, where a spectrum can be formed from each light sensitive pixel. Reinhard Genzel´s group has also played a major role in developing instrumentation for satellites like the Infrared Space Observatory and the future infrared mission Herschel/FIRST of the European Space Agency.
Reinhard Genzel has investigated regions where stars are being formed. He studied water maser sources in the Orion nebula, i.e. clouds containing water molecules that are stimulated by external radiation to emit at certain radio frequencies. By simultaneous observations from radio telescopes on different continents, very high spatial resolution could be achieved.
It seems that galaxies are most likely formed and grow by merging with and cannibalising smaller ones. Many of these objects are the so-called ultraluminous infrared galaxies that emit enormous amounts of energy in the infrared region. Reinhard Genzel and his group have studied the emission features of ultraluminous galaxies using ground-based data and observations with the Infrared Space Observatory.
The centre of our galaxy, at a distance of 25,000 light years, is efficiently obscured from optical telescopes by enormous amounts of dust. However, infrared radiation can penetrate the dust, and Reinhard Genzel began examining the velocities of the gas surrounding the centre. His aim was to use higher and higher resolution to penetrate as close as possible to the centre itself.

Reinhard Genzel’s group showed that the orbits of stars close to the Galactic centre could be measured. They also found that one particular star orbits the central radio source with a velocity exceeding 5,000 km/second and a period to complete a full orbit of only 15 years. The size of this galactic orbit is about the size of the solar system. The concentration of mass is tremendous, and the only conceivable conclusion is that the Galactic centre harbours a so-called black hole with a mass three million times the mass of the sun.

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