Excellent: Stern-Gerlach Medal awarded to Frank Eisenhauer

November 18, 2021

The German Physical Society (DPG) awards the Stern-Gerlach Medal, the DPG's highest award for excellent achievements in experimental physics, to Frank Eisenhauer of the Max Planck Institute for Extraterrestrial Physics (MPE). Frank Eisenhauer is honoured for his "pioneering work in high-resolution infrared astronomy, which has revolutionized spectroscopic as well as astrometric studies."

MPE scientist Frank Eisenhauer

For some twenty years, Frank Eisenhauer has been leading the development of innovative instruments in ground-based infrared astronomy, such as the SINFONI integral-field spectrograph and the GRAVITY interferometer at the Very Large Telescope (VLT) of the European Southern Observatory (ESO)in Chile. These instruments allow astronomers to gain detailed insights into black holes, active galactic nuclei, exoplanets, as well as star and galaxy formation.

In his diploma and PhD theses, which Frank Eisenhauer worked on at MPE, the Technical University Munich and the Ludwig-Maximilians-Universität Munich, he was already building instruments to reach the theoretical resolution limit with telescopes. Soon, he was focussing his research on the Galactic Center and led work on the VLT-instruments SINFONI and GRAVITY to observe the centre of our home galaxy with increasing precision.

With SINFONI, Frank Eisenhauer pioneered the field of imaging spectroscopy. Using a unique combination of adaptive optics and imaging spectroscopy that was unique at the time, SINFONI was not only able to correct for image blurring due to the Earth's atmosphere, but also to record a spectrum for each pixel in the image simultaneously. Thus, in 2003, Eisenhauer and colleagues were able to measure the distance to the centre of the Milky Way from the orbit of a star around the massive black hole by using geometric methods for the first time.

With the GRAVITY experiment, Frank Eisenhauer and his colleagues revolutionised infrared interferometry. Here, the four VLTs are combined to achieve an angular resolution equivalent to that of a telescope with a diameter of 130 meters. Similar to adaptive optics, GRAVITY actively corrects for the perturbing effects of the Earth's atmosphere and disturbances in the light path between the telescope and the laboratory, making GRAVITY several orders of magnitude more sensitive compared to previous experiments. In 2018, Frank Eisenhauer and his colleagues used it to detect – among other things – the gravitational redshift in the gravitational field of the massive black hole predicted by Albert Einstein's theory of general relativity. The very high-resolution observations of the Galactic Center with the GRAVITY interferometer also contributed to the award of the Nobel Prize to Reinhard Genzel in 2020, who is the Director of the Infrared Astronomy Department at MPE.

Gravitational redshift

Artist’s impression of the gravitational redshift of S2 when passing the supermassive black hole at centre of Milky Way.

Currently, Frank Eisenhauer and his group are working on the update GRAVITY+ to increase the sensitivity of the GRAVITY interferometer by another order of magnitude. In addition to his position as senior scientist at MPE, Frank Eisenhauer teaches astrophysics and high-resolution astronomy at the Technical University Munich.

Inside GRAVITY

Animation of the path an incoming light ray traces through the GRAVITY instrument. Note the intricate design and complex interaction of the various components for the four telescopes. For interferometry to work, the light paths have to be superposed with a precision of a fraction of the wavelength – less than 1 micrometre.

The Stern-Gerlach Medal is the DPG's highest award for outstanding achievements in the field of experimental physics. It is awarded for work in the entire field of physics. The Stern-Gerlach Medal was established as a prize by the DPG in 1986 and converted into a medal in 1992. This is the third time that an MPE scientist has received this award, after Joachim Trümper in 1995 and Reinhard Genzel in 2003.

This year, Frank Eisenhauer has already been honoured with the Tycho Brahe Medal, the European Astronomical Society’s highest award for the development and scientific exploitation of astronomical instruments.

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