Press releases


Jun 7 2016

The crucial step takes place in the dark

News about the light-dependent magnetic compass of birds

FRANKFURT. Birds have a light-dependent compass in their eyes. This compass gives them information about the direction of the Earth's magnetic field. Prof. Roswitha Wiltschko's research groupat Goethe University Frankfurt, together with French colleagues, has elucidated how this compass works at the molecular level.

Birds have two sensory organs for orientation and navigation in the Earth's magnetic field: They use their beak to measure the strength of the magnetic field, while their eyes provide directional information. One type of cone photoreceptors in the birds' eyes is sensitive to UV light and also contains a form of the protein cryptochrome. Previous studies of the Frankfurt researchers suggested that most likely it is this protein that enables birds to detect the magnetic field.

A cyclic reaction involving one light-dependent and one light-independent step takes place in the cryptochrome. Two radical pairs are formed during this cycle, and their unpaired valence electrons react to magnetic fields. The Frankfurt group, working in collaboration with Pierre and Marie Curie University Paris, have now discovered which of these two radical pairs is crucial for navigation in the Earth's magnetic field.

In a behavioural study on robins, the birds were subjected to two experimental conditions: (1) at one-second intervals, the researchers switched off either the light or the Earth's magnetic field while keeping the other stimulus constant; (2) the stimuli alternated in one-second intervals, such that light and magnetic field were not present at the same time. Even in the latter condition the birds could still orient along the Earth's magnetic field lines. The group concludes that the light-independent radical pair is responsible for detecting the magnetic field lines. Light is only required to keep the cycle going.

"This is the first proof that the radical pair generated in darkness is the crucial one for the magnetic compass", says Prof. Roswitha Wiltschko. Since in other organisms cryptochrome is used exclusively for the perception of light, the study indicates that there has been a special evolutionary adaptation in birds.

Information:  Prof. Roswitha Wiltschko & Christine Nießner, Institute for Ecology and Diversity, Prof. Wolfgang Wiltschko, Institute for Cell Biology and Neuro Sciences; Phone +49(0)69 798-42119 or +49(0)6032 81206;;


Publication: Wiltschko R, Ahmad M, Nießner C, Gehring D, Wiltschko W. 2016 Light-dependent magnetoreception in birds: the crucial step occurs in the dark.J. R. Soc. Interface 20151010.



May 30 2016

The scent from pine forests cooled the atmosphere/ Publications in Nature and Science

Clouds and climate in the pre-industrial age

FRANKFURTAerosol particles generated by human activity counteract the warming of the earth's atmosphere by greenhouse gases. However, this effect might be smaller than first thought, as many particles were already generated from tree emissions in pre-industrial times. This was the finding of a simulation carried out as part of the international CLOUD experiment, in which researchers from the Goethe University played a major role. The results are published in the form of three papers in the renowned journals "Science" and "Nature".

"These results are the most important so far by the CLOUD experiment at CERN", said CLOUD spokesperson Jasper Kirkby, Honorary Professor at the Goethe University. "When the nucleation and growth of pure biogenic aerosol particles is included in climate models, it should sharpen our understanding of the impact of human activities on clouds and climate."

Professor Joachim Curtius from the Institute for Atmospheric and Environmental Sciences at the Goethe University added: "We believe that the newly discovered process will mean that we will have to reassess cloud formation in earlier times, as there must have been more particles present than we had previously assumed. There would therefore be less of a difference between the situation then and now than previously thought."

The CLOUD experiment is looking at how new aerosol particles form in the atmosphere and their effect on climate. As the aerosol particles increase, as is the case due to human activities, more sunlight is reflected and more cloud droplets form, making the clouds brighter. In order to estimate the cooling effect caused by anthropogenic influences, it is necessary to know the quantities of aerosols present in the pre-industrial age. As direct measurement is not an option, the effects are simulated through reliable laboratory tests such as the CLOUD experiment, and then applied to climate modelling.

In pre-industrial times, the organic compounds emitted by trees were a major contributing factor in the formation of aerosols. The researchers examined alpha-pinene, a substance that gives pine forests their characteristic pleasant smell. They are among the most important biogenic emissions. Alpha-pinene is rapidly oxidised on exposure to ozone and the ensuing reaction chains create some extremely low-volatility substances. However, these only occur in very small concentrations of around one molecule per one trillion air molecules.

The CLOUD experiments show that these extremely low-volatility organic compounds are very efficient at forming new particles. This process occurs under atmospheric conditions, even in the absence of sulphuric acid. It had been assumed that sulphuric acid was virtually always involved in particle formation in the atmosphere. The main source of sulphuric acid in the atmosphere is sulphur dioxide, which is generated by the burning of fossil fuels.

Furthermore, the researchers discovered that ions from cosmic rays strongly enhance the production rate of the organic particles - by a factor of 10-100 compared to particle formation without ions, provided the concentrations of the particle-forming gases are low. "Furthermore, our studies show that these low-volatility organic substances also dominate particle growth in unpolluted environments across the entire size range from clusters of just a few molecules all the way up to sizes of 50-100 nm, where the particles are large enough to be able to seed cloud droplets", explained Joachim Curtius. The growth rates accelerate as the particles increase in size, because more and more oxidation products, also those of higher volatility, are able to condense on the expanding particles. This process is described in quantitative terms with a condensation model for the various organic substances.

Why is this knowledge important for our understanding of the climate? This may well be a very important mechanism, because it is so efficient in terms of the formation of organic particles under natural conditions. As soon as the particles have formed, they grow through the condensation of other similar oxygenated organic compounds. The rapid growth of the newly-formed particles means that they lose a smaller percentage through collisions with pre-existing large particles. As a result more particles grow to sizes that have the potential to seed clouds and influence the climate.

Another paper that appears in the same issue of "Science" reports on observations from the observatory on the Jungfraujoch, which detected pure organic nucleation in the free troposphere. This proves the relevance of the CLOUD laboratory experiments for the atmosphere.


Here you can find an image to download.

Caption (fltr): Mario Simon, Martin Heinritzi, Andreas Kürten, Andrea Wagner and Joachim Curtius with the mass spectrometer they developed. This is used to measure the highly oxygenated multifunctional   organic molecules and molecule clusters, which are responsible for particle generation and particle growth in the recent CLOUD experiments.


Kirkby, J. et al.: Ion-induced nucleation of pure biogenic particles, in: Nature, doi:10.1038/nature17953

Tröstl, J. et al.: The role of low-volatility organic compounds in initial particle growth in the atmosphere, in: Nature, doi:10.1038/nature18271.


Bianchi, F. et al.: New particle formation in the free troposphere: A question of

chemistry and timing, in: Science, doi 10.1126/science.aad5456, 2016

Information: Prof. Dr. Joachim Curtius, Institute for Atmosphere and Environment, Goethe University, Campus Riedberg, Phone +49(0)69 798-40258,


May 9 2016

Five Frankfurt physicists receive the Helmholtz Award with an endowment of Euro 20,000

Award for ground-breaking measuring methods

This year the most important award in the field of metrology, the science of making precise measurements, was awarded to a team of five Frankfurt atomic physicists at Goethe University: Prof. Reinhard Dörner, Associate Prof. Dr. Till Jahnke, Dr. Maksim Kunitzki, Dr. Jörg Voigtsberger and Stefan Zeller. The Helmholtz award includes an endowment of Euro 20,000 and is awarded to European researchers every three years.

The award recipients succeeded in measuring the extremely weak binding energy of helium molecules with a previously unachievable precision. Chemistry teaches us that helium as a noble gas doesn't form bonds. However, this becomes possible under certain circumstances predicted by quantum theory. The study group under Dörner has measured this binding energy indirectly with the COLTRIMS reaction microscope developed at Goethe University. It can be used to measure the location and speed of decaying molecules at the same time with a high level of accuracy, and this data can be used to reconstruct the original configuration. The award winners focused on rare molecules composed of two or three helium atoms.

"It started with the German Research Foundation approving me for a Koselleck project with funding of over 1.25 million in 2009. This is a kind of venture capital, which the DFG uses to support experiments with a long lead time", Prof. Reinhard Dörner from the Institute for Nuclear Physics explains. Dr. Till Jahnke laid the foundation for the equipment, then doctoral candidate Jörg Voigtsberger took over the experiment and achieved initial successes. The next doctoral candidate, Stefan Zeller, was able to make significant improvements to the equipment and to further increase the precision. To do so, he had to direct the largest "photon canon" in Germany, the "Free Electron Laser FLASH" at the DESY research centre in Hamburg, at the extremely weakly bonded helium molecules. In this way he was able to determine the binding energy with a precision of a few nano-electron volts. This means that the binding energy of the helium molecules is one-hundred million times weaker than in a water molecule, for example.

The series of experiments culminated this past year with the dicovery of the so-called Efimov state for a helium molecule made up of three atoms. This comparatively huge molecule predicted 40 years ago by the Russian theorist Vitaly Efimov, can only exist in the tunnel effect established by quantum physics. The postdoc Maksim Kunitzki succeeded in making this measurement with the same equipment.

"All Helmholtz Award winners to date have significantly advanced the art of measuring and many of them are among the most renowned researchers in the field of metrology today", said Dr. Joachim Ullrich, President of the National Metrology Institute of Germany (PTB) and Chairman of the Helmholtz Fund. "We are confident that this will also hold true this time." Researchers at the University of Cambridge are also distinguished with the Helmholtz Award for their method of measuring individual molecules using nano-pores, a proven method in DNA analysis. They have created a method for theoretically detecting any number of different protein molecules in the same measurement. The award will be presented on 22 June 2016 in the conference centre of the National Metrology Institute of Germany (PTB).

The Frankfurt award winners have already received several other rewards for their work: In 2013 Till Jahnke was awarded the most important young scientistaward of the Deutsche Physikalische Gesellschaft, the Gustav Hertz Award. The following year, Reinhard Dörner was distinguished with the renowned Robert Wichard Pohl Award by the Deutsche Physikalische Gesellschaft.In 2015, Maksim Kunitski received an award from the "Frankfurter Förderverein für physikalische Grundlagenforschung".


A picture is available for downloading here:

Caption: Prof. Reinhard Dörner (left) and Maksim Kunitski in front of the equipment used to complete the outstanding work.


Information: Prof. Reinhard Dörner, Institut für Kernphysik, Max-von-Laue-Str. 1, Tel: (069) 798-47003,



Apr 13 2016

Astrophysicists from Goethe University Frankfurt have found a simple formula for the maximum mass of a rotating neutron star

When will a neutron star collapse to a black hole?

Astrophysicists from Goethe-University Frankfurt have found a simple formula for the maximum mass of a rotating neutron star and hence answered a question that had been open for decades. A young women did the analysis during her bachelor thesis.

Neutron stars are the most extreme and fascinating objects known to exist in our universe: Such a star has a mass that is up to twice that of the sun but a radius of only a dozen kilometres: hence it has an enormous density, thousands of billions of times that of the densest element on Earth. An important property of neutron stars, distinguishing them from normal stars, is that their mass cannot grow without bound. Indeed, if a nonrotating star increases its mass, also its density will increase. Normally this will lead to a new equilibrium and the star can live stably in this state for thousands of years. This process, however, cannot repeat indefinitely and the accreting star will reach a mass above which no physical pressure will prevent it from collapsing to a black hole. The critical mass when this happens is called the "maximum mass" and represents an upper limit to the mass that a nonrotating neutron star can be.

However, once the maximum mass is reached, the star also has an alternative to the collapse: it can rotate. A rotating star, in fact, can support a mass larger than if it was nonrotating, simply because the additional centrifugal force can help balance the gravitational force. Also in this case, however, the star cannot be arbitrarily massive because an increase in mass must be accompanied by an increase in rotation and there is a limit to how fast a star can rotate before breaking apart. Hence, for any neutron star there is an absolute maximum mass and is given by the largest mass of the fastest-spinning model.

Determining this value from first principles is difficult because it depends on the equation of state of the matter composing the star and this is still essentially unknown. Because of this, the determination of the maximum rotating mass of a neutron star has been an unsolved problem for decades. This has changed with a recent work published on Monthly Notices of the Royal Astronomical Society, where it has been found that it is indeed possible to predict the maximum mass a rapidly rotating neutron star can attain by simply considering what is maximum mass of corresponding the nonrotating configuration.

"It is quite remarkable that a system as complex as a rotating neutron star can be described by such a simple relation", declares Prof. Luciano Rezzolla, one of the authors of the publication and Chair of Theoretical Astrophysics at the Goethe University in Frankfurt. "Surprisingly, we now know that even the fastest rotation can at most increase the maximum mass of 20% at most", remarks Rezzolla.

Although a very large number of stellar models have been computed to obtain this result, what was essential in this discovery was to look at this data in proper way. More specifically, it was necessary to realise that if represented with a proper normalisation, the data behaves in a universal manner, that is, in a way that is essentially independent of the equation of state.

"This result has always been in front of our eyes, but we needed to look at it from the right perspective to actually see it", says Cosima Breu, a Master student at the University of Frankfurt, who has performed the analysis of the data during her Bachelor thesis.

The universal behaviour found for the maximum mass is part of a larger class of universal relations found recently for neutron stars. Within this context, Breu and Rezzolla have also proposed an improved way to express the moment of inertia of these rotating stars in terms of their compactness. Once observations of the moment of inertia will be possible through the measurement of binary pulsars, the new method will allow us to measure the stellar radius with a precision of 10% or less.

This simple but powerful result opens the prospects for more universal relations to be found in rotating stars. "We hope to find more equally exciting results when studying the largely unexplored grounds of differentially rotating neutron stars", concludes Rezzolla.

Publication: Cosima Breu, Luciano Rezzolla: Maximum mass, moment of inertia and compactness of relativistic, in: Monthly Notices of the Royal Astronomical Society;doi: 10.1093/mnras/stw575

Interview with Cosima Breu und Luciano Rezzolla on Goethe-Uni online (in German):


Images for download:


Contact: Prof. Luciano Rezzolla, Institute for Theoretical Physics, Goethe University Frankfurt, Tel,: + 49 69 798 47871,



Apr 1 2016

Researchers develop organoids from insulin-producing cells for transplantation

EU project aims to cure type 1 diabetes

FRANKFURT.The number of children in Europe and the USA with type 1 diabetes is growing by four percent each year. A group of European researchers has now joined forces under the leadership of the Goethe University, with the goal of sparing affected people from lifelong insulin therapy. They plan to develop three-dimensional cellular structures of insulin-producing cells (organoids) in the laboratory and to work with pharmaceutical industry partners to develop a process for their mass production. The European Union is providing over five million Euro over the next four years to support the project. The first clinical studies on transplantation of organoids are planned after that.

Patients with type 1 diabetes are unable to produce insulin due to a genetic defect or an autoimmune disorder. They could be cured by transplanting a functional pancreas, but there are not nearly enough donor organs available. This is why researchers had the idea of growing intact insulin-producing cells from donor organs in the laboratory to form organoids, which they would then transplant into the pancreas of diabetes patients. "The method has already been shown to work in mice", explains Dr Francesco Pampaloni, who coordinated the first project together with Prof. Ernst Stelzer at the Buchmann Institute for Molecular Life Sciences at the Goethe University.

Researchers have only recently discovered how to produce organoids. Adult stem cells, which develop into cells for wound healing or tissue regeneration in the body, are the starting point. These cells can be grown in the laboratory through cell division and then allowed to differentiate into the desired cell type. The key is now to embed them in a matrix so that they grow into three-dimensional structures. The organoids are typically spherical, hollow on the inside and have a diameter of approx. 20 micrometres – about half as thick as the diameter of a human hair – to hundreds of micrometres. "If the structure were compact, then there would be a risk of the inner cells dying off after transplantation because they wouldn't be supplied by the host organ's cellular tissue", Pampaloni explains.

The task of the Frankfurt group under Stelzer and Pampaloni is to control the growth and differentiation of the filigree organoids under a microscope. To do so, they use a light microscopy method developed by Stelzer with which the growth of biological objects can be followed cell for cell in three dimensions. The project is called LSFM4Life, because light sheet fluorescence microscopy (LSFM) plays a key role in the project.

The Frankfurt group is also responsible for developing quality assurance protocols, because of the cooperation with industrial partners in Germany, France, the Netherlands and Switzerland, the original goal of the project is the large-scale production of organoids in accordance with good manufacturing practices for pharmaceuticals. Two research groups in Cambridge specialise in isolating insulin-producing cells from donor organs and growing organoids, while a group of clinicians in Milan is developing methods for transplanting organoids.

As is the case for all organ transplants, care will have to be taken with organoids as well so that rejection responses by the recipient's immune system are avoided. However, over time the researchers plan to build cell banks from which immunologically compatible cell types can be selected for every recipient.



Caption: Mouse Pancreas Organoid imaged with a Digitally Scanned Light Sheet-based Fluorescence Microscope (LSFM, mDSLM). Left: actin cytoskeleton (staining Phalloidin-Alexa488). Right: cell nuclei (staining Draq5). Illumination objective lens Carl Zeiss Epiplan Neofluar 2.5x, NA 0.05. Detection objective lens Carl Zeiss W N-Achroplan 10x, NA 0.3. Imaging and visualization by Francesco Pampaloni, Goethe University Frankfurt, BMLS. Pancreas organoids from Meritxell Huch and Christopher Hindley, Gurdon Institute, Cambridge, UK


Information: Dr. Francesco Pampaloni, Buchmann Institute for Molecular Life Sciences, Campus Riedberg, Tel,: (069) 798 42544,