Press releases – 2019

Whether it is new and groundbreaking research results, university topics or events – in our press releases you can find everything you need to know about the happenings at Goethe University. To subscribe, just send an email to

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Oct 1 2019

Physicists at Goethe University measure miniscule effect with new super COLTRIMS apparatus / Publication in Nature Physics

Beyond Einstein: Mystery surrounding photon momentum solved

FRANKFURT. Albert Einstein received the Nobel Prize for explaining the photoelectric effect: in its most intuitive form, a single atom is irradiated with light. According to Einstein, light consists of particles (photons) that transfer only quantised energy to the electron of the atom. If the photon's energy is sufficient, it knocks the electrons out of the atom. But what happens to the photon's momentum in this process? Physicists at Goethe University are now able to answer this question. To do so, they developed and constructed and new spectrometer with previously unattainable resolution. 

Doctoral student Alexander Hartung became a father twice during the construction of the apparatus. The device, which is three meters long and 2.5 meters high, contains approximately as many parts as an automobile. It sits in the experiment hall of the Physics building on Riedberg Campus, surrounded by an opaque, black tent inside which is an extremely high performing laser. Its photons collide with individual argon atoms in the apparatus, and thereby remove one electron from each of the atoms. The momentum of these electrons at the time of their appearance is measured with extreme precision in a long tube of the apparatus. 

The device is a further development of the COLTRIMS principle that was invented in Frankfurt and has meanwhile spread across the world: it consists of ionising individual atoms, or breaking up molecules, and then precisely determining the momentum of the particles. However, the transfer of the photon momentum to electrons predicted by theoretic calculations is so tiny that it was previously not possible to measure it. And this is why Hartung built the “super COLTRIMS". 

When numerous photons from a laser pulse bombard an argon atom, they ionise it. Breaking up the atom partially consumes the photon's energy. The remaining energy is transferred to the released electron. The question of which reaction partner (electron or atom nucleus) conserves the momentum of the photon has occupied physicists for over 30 years. “The simplest idea is this: as long as the electron is attached to the nucleus, the momentum is transferred to the heavier particle, i.e., the atom nucleus. As soon as it breaks free, the photon momentum is transferred to the electron," explains Hartung's supervisor, Professor Reinhard Dörner from the Institute for Nuclear Physics. This would be analogous to wind transferring its momentum to the sail of a boat. As long as the sail is firmly attached, the wind's momentum propels the boat forward. The instant the ropes tear, however, the wind's momentum is transferred to the sail alone. 

However, the answer that Alexander Hartung discovered through his experiment is – as is typical for quantum mechanics - more surprising. The electron not only receives the expected momentum, but additionally one third of the photon momentum that actually should have gone to the atom nucleus. The sail of the boat therefore “knows" of the impending accident before the cords tear and steals a bit of the boat's momentum. To explain the result more precisely, 

Hartung uses the concept of light as an electro-magnetic wave: “We know that the electrons tunnel through a small energy barrier. In doing so, they are pulled away from the nucleus by the strong electric field of the laser, while the magnetic field transfers this additional momentum to the electrons." Hartung used a clever measuring setup for the experiment. To ensure that the small additional momentum of the electron was not caused accidentally by an asymmetry in the apparatus, he had the laser pulse hit the gas from two sides: either from the right or the left, and then from both directions simultaneously, which was the biggest challenge for the measuring technique. This new method of precision measurement promises deeper understanding of the previously unexplored role of the magnetic components of laser light in atomic physics.

Images may be downloaded here:
Image 1: Photo of the COLTRIMS reaction microscope built by Alexander Hartung as part of his doctoral research in the experiment hall of the Faculty of Physics. Credit: Alexander Hartung
Image 2:Technical drawing of the newly constructed COLTRIMS reaction microscope. The drawing shows an intersection of the experimental construction. Individual gas atoms, which fly down through the vertical tube in the picture, are ionised by a highly intensive laser. The beam path of the laser is illustrated on the table in the back. The momenta of the electrons and ions that are produced in the reaction are measured with extreme precision by the horizontally depicted bronze-coloured spectrometer in the vacuum chamber. In this way, the effect of the miniscule momentum of the ionised laser light on the electrons can be studied precisely. Credit: Alexander Hartung 

Publication: A. Hartung, S. Eckart, S. Brennecke, J. Rist, D. Trabert, K. Fehre, M. Richter, H. Sann, S. Zeller, K. Henrichs, G. Kastirke, J. Hoehl, A. Kalinin, M. S. Schöffler, T. Jahnke, L. Ph. H. Schmidt, M. Lein, M. Kunitski, R. Dörner: Magnetic fields alter tunneling in strong-field ionization, in: Nature Physics, doi: 10.1038/s41567-019-0653-y. 

Further information: Professor Reinhard Dörner, Alexander Hartung, Institute for Nuclear Physics, Faculty of Physics, Riedberg Campus, Phone.: +49 69 798-47003 or -47019; Email: doerner[at] or hartung[at]


Sep 16 2019

Sleep or stop? The RIS neuron has both functions / Publication in Nature Communications

The sleep neuron in threadworms is also a stop neuron

FRANKFURT. The nervous system of the threadworm C. elegans is simple at first sight: it consists of 302 neurons, some of which, however, have several functions. The neuron “RIS", known as a sleep neuron, can therefore put the worm into a long sleep – or also just briefly stop its locomotion, as a group of scientists led by Goethe University have now discovered. 

Wagner Steuer Costa in the team of Alexander Gottschalk, Professor for Molecular Cell Biology and Neurobiochemistry, discovered the sleep neuron RIS a few years ago by coincidence – simultaneously with other groups. To understand the function of individual neurons in the plexus, the researchers use genetic engineering to cause them to produce light-sensitive proteins. With these “photo-switches", the neurons can be activated or turned off in the transparent worm using light radiation of a certain wavelength. “When we saw that the worm froze when this neuron was stimulated by light, we were quite amazed. It was the beginning of a study that took several years," Gottschalk recalls. 

The RIS neuron puts C. elegans to sleep when it is active for minutes or hours – for example after the shedding of the cuticle (a secreted form of skin) that is a process in the animal's development. It also sleeps in order to recover after experiencing cellular stress. On the other hand, the neuron serves to stop the worm during locomotion – for example, if it wants to change direction or to avoid danger. The neuron then slows down the animal's motion so that it has time to decide if it wants to continue crawling. In this case the neuron is only active for a few seconds. “Such stop neurons have only recently been discovered. This is the first one of its kind in a worm," explains Gottschalk. 

Interestingly, the axon of the RIS neuron is apparently branched, with the two branches having different functions, so that RIS not only slows motions but can also introduce backwards motion. This is reported by Gottschalk and his collaboration partners, Professor Ernst Stelzer from Goethe University, Professor Sabine Fischer from the University of Würzburg, researchers from the American Vanderbilt University in Nashville and KU Leuven in the current issue of “Nature Communications". 

“We think that neurons with a double function exist in numerous simple life forms such as the worm. In the course of evolution they were then assigned to two different systems in the brain and further developed," says Gottschalk. It's a theme that will certainly be found to recur once other nerve cells of the worm are better understood. “The nervous system of C. elegans can be viewed as a kind of evolutionary test bed. If it works there, it will be used again and further refined in more complex animals." 

The discovery of the double function of RIS is also an example of how a permanently connected neuronal network can be additionally operated by a “wireless" network of neuropeptides and neuromodulators. This enables several functional networks to be realised on a single anatomical network, enormously increasing the functionality of the worm's brain, as well as being very economical. “It should no longer be said that worm neurons are simple. Often, they can do more than mammalian neurons," says Gottschalk. 

Publication: Wagner Steuer Costa, Petrus Van der Auwera, Caspar Glock, Jana F. Liewald, Maximilian Bach, Christina Schüler, Sebastian Wabnig, Alexandra Oranth, Florentin Masurat, Henrik Bringmann, Liliane Schoofs, Ernst H.K. Stelzer, Sabine C. Fischer, Alexander Gottschalk: A GABAergic and peptidergic sleep neuron as a locomotion stop neuron with compartmentalized Ca2+ dynamics 

Images may be downloaded at:
Caption (1): The threadworm C. elegans. Credit: A. Gottschalk
Caption (2): The RIS neuron (green) in the throat of the threadworm C. elegans. Credit: Wagner Steuer Costa
Interesting videos can also be viewed on the Nature Communications website, e.g.. #7: 

Further information: Prof. Dr. Alexander Gottschalk, Molecular Cell Biology and Neurobiology and Institute for Biophysical Chemistry, Faculty of Biochemistry, Chemistry and Pharmacy, and Buchmann Institute for Molecular Life Sciences, Riedberg Campus, Tel.: +49 069 798-42518 , Email:


Sep 12 2019

Ozone hole, fires in the Amazon, and gravity waves are focus of German research aircraft HALO

Climate change in the Southern Hemisphere 

FRANKFURT. On its mission “SouthTRAC", the German research aircraft HALO will investigate the southern atmosphere and its effects on climate change in September and November 2019. Researchers from Goethe University will also be on board. 

The most important goal of the first phase of the SouthTRAC (Transport and Composition of the Southern Hemisphere UTLS) campaign is to investigate gravity waves on the southern tip of South America and over Antarctica. The second phase of the campaign in November will focus on the exchange of air masses between the stratosphere and the troposphere. During the transfer flights between Europe and South America, the scientists will also investigate the influence of the current fires in the Amazon rainforest on climate. In addition to the team of the atmosphere researcher Professor Andreas Engel from Goethe University, researchers from the German Aerospace Center (DLR), the Karlsruhe Institute of Technology (KIT), the research centre Jülich, and University Mainz have been in charge of the scientific planning. Groups from the Universities in Heidelberg and Wuppertal are also involved. 

Trace gases such as ozone and steam are effective greenhouse gases, and play an important role in climate change. Since the end of the 1980's, the Montreal Protocol regulates substances such as chlorofluorocarbons (CFC) because they thin out the ozone layer. It will take many decades, however, for the ozone layer to recover, especially the large ozone hole in Antarctica. In the campaign “SouthTRAC", researchers now want to investigate in detail what this means for climate change in the Southern Hemisphere. 

In addition to high levels of chlorine and bromine, the most important atmospheric requirements for the formation of the ozone hole above Antarctica are low temperatures and a reduced exchange of air masses with mid-latitudes. The Antarctic polar vortex is responsible for this. “We want to see how much chlorine and bromine is available to deplete the ozone in the lower stratosphere, especially in the polar vortex of the Southern Hemisphere, where the ozone hole is formed every year," explains Professor Andreas Engel. To do this, his group measures almost all relevant source gases. They pay special attention to short-lived substances that are highly variable and have hardly been quantified in the Southern Hemisphere so far. “We want to make data available so that chemical and climate models can more reliably portray the depletion of the ozone, the expected recovery of the stratospheric ozone, and the effects on climate," says the atmospheric researcher.

For this purpose, Professor Andreas Engel's team at the Institute for Atmosphere and Environment at Goethe University uses a gas chromatograph with mass spectrometer they developed themselves. This instrument can measure even traces of many chlorinated and brominated substances, although the measuring speed also has to be taken into account. On board a research aircraft things have to go quickly, because the resolution in time corresponds directly with the resolution in space. “At one to six minutes, depending on the substances, we're extremely fast for this measuring technique. In the lab, it takes almost five times as long. And everything we do in an aircraft has to be certified for air worthiness on top of it all. That requires a significant logistical effort," says Engel. 

In order to make these difficult measurements possible, some of which have to be carried out during a night shift, three to five members of the Institute for Atmosphere and Environment will be on location in Rio Grande on the southern tip of South America until the beginning of December, with a short break of three weeks in October. The measuring flights depart from here, and this is where the measuring instruments are taken care of as well. 

About HALO
The research aircraft HALO (High Altitude and Long Range) is a collaborative initiative of German environmental and climate research institutions. It is funded by grants from the Federal Ministry of Education and Research (BMBF), the Deutsche Forschungsgemeinschaft (DFG), the Heimholtz Association, the Max Planck Society, the Leibniz Association, the State of Bavaria, the Karlsruhe Institute of Technology (KIT), the research centre Jülich and the German Aerospace Center (DLR).

Images may be downloaded here:
Credit: See ending of file names.

Further information: Professor Andreas Engel, Institute for Atmosphere and Environment, Faculty of Geosciences, Riedberg Campus, phone: +49 69 798-40259,


Sep 9 2019

Professor Luciano Rezzolla and his team, together with 347 researchers from the worldwide Event Horizon Telescope Collaboration, have been awarded the Breakthrough Prize 2020 in recognition of their ground-breaking achievements

Black Hole: Important global award for astrophysicists at Goethe University

FRANKFURT. For their exceptional and fundamental achievements in capturing the first direct image of a black hole, researchers from the team headed by astrophysicist Professor Luciano Rezzolla of Goethe University, together with 347 scientists from the global Event Horizon Telescope Collaboration, will receive the Breakthrough Prize 2020, which comes with $ 3 million in prize money. With its 10 members, the Goethe University team is one of the largest in the entire collaboration, which comprises 140 institutions in total. 

With the aid of eight radio telescopes around the world, to which meanwhile another three have been added, the scientists succeeded in capturing the first direct visual evidence of the supermassive black hole at the centre of the galaxy Messier 87 in April 2019. The prize will be distributed equally among all the co-authors of the corresponding scientific publications, and will be awarded on 3rd November. 

Luciano Rezzolla's team made fundamental contributions to the theoretical interpretation of the results throughout all phases of the observations: using supercomputers, they simulated how material forms a ring-shaped disc as it orbits and is pulled into the black hole, and how the tremendous gravitation bends light rays around the black hole. It was also necessary to rule out various alternatives to black holes that are also compatible with the theory of relativity. “The confrontation of theory with observations is always a dramatic moment for a theoretical physicist. We were quite relieved, and also proud, that the observations matched our predictions so well," states Luciano Rezzolla. 

Goethe University President Professor Dr. Birgitta Wolff: “Together with Luciano Rezzolla and his team, we are delighted about this important global award. We warmly congratulate all of our colleagues who contributed to this achievement! We remember the enthusiasm of audience in the packed lecture hall on Campus Riedberg when Luciano Rezzolla and his colleagues from the European Consortium (Professor Michael Kramer from the Max Planck Institut für Radioastronomie in Bonn and Professor Heino Falcke from the Dutch Radboud University) first presented the results of their joint research at Goethe University on 17th  April 2019. It was a celebration of the power of fascination emanating even from abstract science. I hope that further ground-breaking research will be forthcoming from this great global collaboration." 

Goethe University Vice-President Professor Simone Fulda, who is responsible for research, said: “We are proud to have played such a prominent role as Goethe University in a true scientific breakthrough of global significance and congratulate Luciano Rezzolla and his team for the outstanding achievements that led to it. Physics is an important research focal point that has shaped Goethe University's research profile for many years." 

“It's a great honour and an enormous gratification to see that the work done at Goethe University has received the highest recognition and has contributed to pushing the limits of our understanding of fundamental physics. It is also a fair recognition of what has ultimately been a team effort and hence a shared burden and challenge of many scientists across the world," commented Luciano Rezzolla. 

As a collective, this year's Breakthrough Prize laureates probed the galaxies to capture the first image of a black hole. The jury has found remarkable the achievements by combining telescope after synchronizing them with atomic clocks, producing a virtual telescope as large as the Earth, to obtain unprecedented resolution. The image of the supermassive black hole at the centre of the Messier 87 galaxy was obtained after painstakingly analysing the data with novel algorithms and techniques, and reveals a bright ring marking the point where light orbits the black hole, surrounding a dark region where light cannot escape the black hole's gravitational pull. The black hole shadow matched the expectations of Einstein's theory of General Relativity. 

Collaboration Director Shep Doeleman of the Harvard-Smithsonian Center for Astrophysics, who will accept the prize on behalf of the collaboration at the ceremony on 3rd November 2019, says: "We set out to see the unseeable, and we needed to build a telescope as large as the Earth to do it. It sounds like science fiction, but we assembled an incredible global team of experts and used the most advanced radio telescopes on the planet to make it a reality. This breakthrough prize celebrates a new beginning in our study of black holes."

The “Breakthrough Prize Foundation" has prominent backers. Its founding members are Sergey Brin, Priscilla Chan and Mark Zuckerberg, Ma Huateng, Yuri und Julia Milner, and Anne Wojcicki. 

Press release on the image of the black hole from 10th April 2019.  
Film material on the black hole (Simulations and background on the research at Goethe University) can be found here:
How we made the black hole visible. Short version 
How we made the black hole visible. Long version with personal statements
Simulations of the shadow of a black hole (English)
Simulations of the shadow of a black hole (Spanish) 

Further information: Prof. Luciano Rezzolla, Principal Investigator of the European Black Hole Cam Experiments, Institute for Theoretical Physcis, Faculty of Physics, Riedberg Campus, Telefon: +49 69 798 47871:,;


Sep 5 2019

Commemorates heyday period in the 1920s 

“Historic Site” Plaque for Frankfurt Physics 

FRANKFURT. The 1920s were the golden age of quantum mechanics. Brilliant theoreticians and young, innovative thinkers poured the theory into its modern mathematical form. Their predictions inspired new experiments. At the Physics Institute of Frankfurt University headed by Max Born, physicists Otto Stern and Walter Gerlach made important contributions using a new experimental method. This will be commemorated by a “historic site" plaque that was unveiled Tuesday in a ceremony in the historic auditorium of the Jügelhaus, formerly the main Goethe University building on Bockenheim Campus. Once the Historical Monument Department has approved, the plaque will be mounted onto the former physics building at Robert-Mayer-Straße 2. 

“Everyone is familiar with Goethe, but Nobel Prize winner Otto Stern is still largely unknown,“ comments University President Birgitta Wolff. “The university named its new auditorium complex on Riedberg Campus after Otto Stern a few years ago. I'm delighted that a Historic Site Plaque now marks the location where Otto Stern succeeded with his pioneering experiments." 

The “historic site" plaque is awarded by the European Physical Society to commemorate important discoveries in physics in laboratories, institutes or cities throughout Europe. The former Institute of Theoretical Physics building in Frankfurt is the fourth location in Germany to be distinguished with this plaque. 

“The year 2019 presents a two-fold opportunity to remember the pioneer of quantum physics and Nobel Laureate Otto Stern," explains physics professor Horst Schmidt-Böcking, who authored a biography of Otto Stern together with the historian Karin Reich. In 1919, Otto Stern developed the molecular beam method, for which he received the Nobel Prize for Physics in 1943. In the iconic Stern-Gerlach experiment, completed in February 1922, the reality of space quantization of angular momentum had been demonstrated. The momentum resolution achieved corresponded to an energy resolution of a micro electron volt. In 1922, together with Walther Gerlach in the iconic Stern-Gerlach experiment, the reality of space quantization of angular momentum was demonstrated, also proving the angular momentum quantization in atoms for the first time. “At the same time, we commemorate the 50th anniversary of Otto Stern's death, who was forced to emigrate in 1933 because of his Jewish background," remarks Schmidt-Böcking. 

Otto Stern first settled in Pittsburgh and then Berkeley in 1945. In contrast to many other emigrants, he took every opportunity after the Second World War to meet with friends and colleagues at conferences in Europe. Horst Schmidt-Böcking has been in contact with Otto Stern's descendants in the United States in recent years and invited them to visit their uncle's old domain. Stern himself had no children. 

“The Historic Site Plaque also commemorates other important discoveries made at the Physics Institute," says Petra Rudolf, President of the European Physical Society. “In 1920 Max Born and Elisabeth Bormann first measured the free path of atoms in gases and the size of molecules. In 1921, the theoretician Alfred Landé postulated the coupling of angular momentum for the first time as the basis of intra-atomic electron dynamics." 

An international conference commemorating Otto Stern is taking place this week, as Wilhelm and Else Heraeus Seminar entitled “Otto Stern's Molecular Beam Research and its Impact on Science". Speakers include people who knew Stern such as his nephew Allen Templeton, scientific historians, and researchers whose experimental methods are based on the molecular beam method developed by Stern, such as magnetic resonance imaging, lasers and masers. The conference goes until 5th September. 

Today, the historical building is home to the Physical Association of Frankfurt. Founded in 1824, it is the oldest one in Germany and was already in existence in 1914 when the university opened. 

Further information: Dr. Horst Schmidt-Böcking, Institut für Kernphysik, Fachbereich Physik, Riedberg Campus, Tel.: +49 69 798 47002,