Astrophysicists at Goethe University Frankfurt set a new limit for the maximum mass of neutron stars: It cannot exceed 2.16 solar masses
FRANKFURT. Since their discovery in the 1960s, scientists have sought to answer an important question: How massive can neutron stars actually become? By contrast to black holes, these stars cannot gain in mass arbitrarily; past a certain limit there is no physical force in nature that can counter their enormous gravitational force. For the first time, astrophysicists at Goethe University Frankfurt have succeeded in calculating a strict upper limit for the maximum mass of neutron stars.
With a radius of about twelve kilometres and a mass that can be twice as large as that of the sun, neutron stars are amongst the densest objects in the Universe, producing gravitational fields comparable to those of black holes. Whilst most neutron stars have a mass of around 1.4 times that of the sun, massive examples are also known, such as the pulsar PSR J0348+0432 with 2.01 solar masses.
The density of these stars is enormous, as if the entire Himalayas were compressed into a beer mug. However, there are indications that a neutron star with a maximum mass would collapse to a black hole if even just a single neutron were added.
Together with his students Elias Most and Lukas Weih, Professor Luciano Rezzolla, physicist, senior fellow at the Frankfurt Institute for Advanced Studies (FIAS) and professor of Theoretical Astrophysics at Goethe University Frankfurt, has now solved the problem that had remained unanswered for 40 years: With an accuracy of a few percent, the maximum mass of non-rotating neutron stars cannot exceed 2.16 solar masses.
The basis for this result was the “universal relations” approach developed in Frankfurt a few years ago [http://www.goethe-university-frankfurt.de/60913695/15]. The existence of “universal relations” implies that practically all neutron stars “look alike”, meaning that their properties can be expressed in terms of dimensionless quantities. The researchers combined these “universal relations” with data on gravitational-wave signals and the subsequent electromagnetic radiation (kilonova) obtained during the observation last year of two merging neutron stars in the framework of the LIGO experiment. This simplifies calculations tremendously because it makes them independent of the equation of state. This equation is a theoretical model for describing dense matter inside a star that provides information on its composition at various depths in the star. Such a universal relation therefore played an essential role in defining the new maximum mass.
The result is a good example of the interaction between theoretical and experimental research. “The beauty of theoretical research is that it can make predictions. Theory, however, desperately needs experiments to narrow down some of its uncertainties,” says Professor Rezzolla. “It’s therefore quite remarkable that the observation of a single binary neutron star merger that occurred millions of light years away combined with the universal relations discovered through our theoretical work have allowed us to solve a riddle that has seen so much speculation in the past.”
The research results were published as a Letter of The Astrophysical Journal. Just a few days later, research groups from the USA and Japan confirmed the findings, despite having so far followed different and independent approaches.
Gravitational-wave astronomy is expected to observe more such events in the near future, both in terms of gravitational-wave signals and in the more traditional frequency ranges. This will further reduce uncertainties about maximum mass and lead to a better understanding of matter under extreme conditions. This will be simulated in modern particle accelerators, for example at CERN in Switzerland or the FAIR facility in Germany.
Publication: Luciano Rezzolla, Elias R. Most, Lukas R. Weih: Using Gravitational-wave Observations and Quasi-universal Relations to Constrain the Maximum Mass of Neutron Stars, The Astrophysical Journal Letters, Volume 852, Number 2, http://iopscience.iop.org/article/10.3847/2041-8213/aaa401, DOI: 10.3847/2041-8213/aaa401
A picture can be downloaded from: www.uni-frankfurt.de/69863080
Caption: Gravitational-wave emission from a collapsing star
Further information: Prof. Luciano Rezzolla, Institute of Theoretical Physics, Riedberg Campus, Tel.: +49(0)69 798-47871, firstname.lastname@example.org
German Research Foundation awards further € 1.5 million for long-term project at Goethe University Frankfurt
FRANKFURT. Goethe University Frankfurt can continue its study of the Nok Culture. The German Research Foundation has recently approved the funding application submitted by Professor Peter Breunig, Professor of African Archaeology, and Professor Katharina Neumann, Professor of African Archaeobotany. This means that an additional € 1.5 million are available to complete the project, which explores the 2,500-year-old West African culture.
The long-term project, which is designed to take a total of twelve years, has been examining all the main aspects of the Nigerian Nok Culture since 2009. The researchers from Frankfurt are working on site alongside their Nigerian colleagues and have also employed a large number of local helpers. At times, the project was the largest employer in the area. Surveys, excavations and extensive data analysis are making a significant contribution to deeper knowledge of chronology, settlement, land use and environment, iron metallurgy, material culture and geographical range.
Peter Breunig is very pleased about the merry pre-Christmas news that the project will be funded right through to the end: “It really is something very special for an archaeologist when you can conduct such extensive research over many years and with a large team thanks to such broad support.” The Nok project is outstanding in terms of content too: not many projects worldwide are set out to explore an entire archaeological culture.
The Nok Culture, which lasted for about 1,500 years and is named after the small village of Nok to the north-east of Abuja, the capital city, emerged around 1500 BC. This is also one of the things that the project has unearthed. At that time, the population lived in simple farming communities and its most important crop was pearl millet. The ornate terracotta figures, for which the Nok Culture is known outside the archaeological world too, emerged 600 years later, i.e. around 900 BC. Looting had already brought many to light before the Frankfurt researchers got to work – the statuettes are coveted objects on the international art market. “The fired clay sculptures represent the oldest and some of the largest examples of figurine art in sub-Saharan Africa,” explains Breunig.
What purpose did the terracottas serve, some of which portray people and others animals? What was their original function when they were made about 2,500 years ago? This has been one of the main questions over the last nine years. The researchers presumed that the figures played a role in burial rites. And indeed, at some sites they were able to locate features interpreted as graves near the terracottas, for example in Ifana where they found around 20. “The custom of making a clay effigy of a deceased dignitary and placing it on the grave still exists in West Africa today. When the figures have weathered, they are all buried together at the same spot,” say Professor Breunig. Perhaps it was the same back then.
The researchers have gained many other important insights besides that. “We know how the Nok people settled, what their pottery looked like, that it was travelling craftsmen who made the terracottas,” says Breunig. And thanks to close cooperation with archaeobotanist Professor Katharina Neumann, the researchers also know what they ate and how their surrounding landscape changed over the course of time. The decline of the Nok Culture began around 400 BC; terracottas and Nok ceramics finally disappeared at the latest by the birth of Christ.
After Breunig and a member of his team were kidnapped in February 2017, the team has returned to Africa only once and did not venture beyond the capital. “But we’ve finished our field research anyway. We’ve got enough to do in the next three years,” explains Breunig. The focus now is on the last remaining studies and publications on settlement, structure and chronology of the sites and the material culture as well as analysis, classification and long-term storage and accessibility of the data. In view of the extensive excavations, volume of data obtained, modern methods applied, countless carbon 14 dating results and the breadth of topics examined, the Nok Culture numbers - thanks to this project - amongst the most thoroughly investigated archaeological complexes in West Africa.
The archaeobotanical research work led by Professor Neumann also plays a prominent role in the project. Her objective is to design a model for vegetation development as well as resource and land use in the Nok region from the beginning of the Nok Culture around 1500 BC up until the first centuries AD. With the help of botanical macroremains and analysis of the chemical residues found in ceramics, her team is examining how the early Nok population adapted to a new habitat, how overexploitation in the Middle Nok period (900 to 400 BC) led to soil degradation and what role this might have played in the decline of the Nok Culture after 400 BC.
The Research Unit “Ecological and Cultural Change in West and Central Africa” funded by the German Research Foundation had already conducted initial research work related to the project from 2005 onwards. The long-term project then entered its first phase shortly after the global conference on African archaeology at Goethe University Frankfurt in 2008, which was opened by Namadi Sambo, later vice-president of Nigeria. One of the highlights was undoubtedly the much acclaimed exhibition “Nok – African sculpture in archaeological context” in 2013/14 at the Liebieghaus Museum in Frankfurt, which was also financed by the German Research Foundation. Since this year, the exhibits are on display at Kaduna National Museum under the title “NOK Within the Context of Nigerian Art Traditions”. All materials which were brought to Frankfurt for research purposes are also returned to Nigeria.
Amongst others, a workshop is planned for the last phase of the project that aims to position Nok ceramics within a broader West African context. By comparing ceramics from other West African regions, the researchers hope to find further answers to the question of where the Nok people came from and how they lived.
Pictures and captions can be downloaded from www.uni-frankfurt.de/69782102
Further information: Professor Peter Breunig, Institute of Archaeological Sciences, Department of African Archaeology and Archaeobotany, Westend Campus, Tel.: +49(0)69-798-32094, email email@example.com
Professor Döll, hydrologist, gets to the bottom of global freshwater system / Legal scholars and economists explore how regulatory framework influences financial market
FRANKFURT. The initiators behind two projects at Goethe University Frankfurt have every reason to be pleased: Their new research groups will benefit from German Research Foundation funds totalling € 1.9 million. Together with her team, Professor Petra Döll, hydrologist, will now be able to explore the global freshwater system in greater depth whilst Professor Tobias Tröger, legal scholar, and Professor Rainer Haselmann, economist, will join forces with fellow researchers to examine how regulatory parameters influence decisions in the financial sector.
“The two new research groups funded by the German Research Foundation show how Goethe University Frankfurt is tackling topics which are socially relevant and of global significance, such as the earth’s water resources and the effects of regulatory measures on market development,” says Professor Birgitta Wolff, the University’s president. “Congratulations to the researchers responsible, Petra Döll, Tobias Tröger and Rainer Haselmann, whose proposals were able to convince the German Research Foundation of the scientific quality of their projects.”
How water is distributed on our planet
The Research Unit “Understanding the Global Freshwater System by Combining Geodetic and Remote Sensing Information with Modelling Using Calibration/Data Assimilation Approach” (GlobalCDA), coordinated by Professor Petra Döll, hydrologist in Frankfurt, and Professor Jürgen Kusche, geodesist in Bonn, has set itself the task of quantifying water flows and water volumes on the earth’s continents more accurately in order to gain a deeper understanding of global water cycles. In fact, global hydrological models already exist, but the aim now is to include additional, satellite-based observation data. “In order to quantify more precisely how water is distributed worldwide, we need to develop a new method that lets us assimilate these data and use them to adjust model parameters,” says Professor Döll, who focuses on further developing the global hydrological WaterGAP that is suitable for estimating the current status and future development of the global freshwater system under human impacts.
Professor Döll has been working since 1996 on global-scale modelling of water resources and their use under the impact of global change. How much water is there in the ground? How much water is flowing in various rivers? And how much water is hidden in snow fields? “If we can understand the present status of water resources and know how water moves, how it is stored and what happens when there is little rainfall, then we are a big step further,” says Döll. Continental water flows play an important role for other aspects of the earth system. For example, groundwater depletion contributes to the global sea level rise. In a globalised world, a better understanding of the freshwater system worldwide would help to ensure sustainable water management (e.g., during droughts), but equally the sustainable production of food and energy. Seven groups from Germany are engaged in the project as well as one from Switzerland and another from Luxembourg. The German researchers will receive a total of about € 1.9 million for the first three years.
How markets react to new regulations
Under the title “Foundations of Law and Finance”, a Centre for Advanced Studies led by law professor Tobias Tröger and economics professor Rainer Haselmann will investigate how institutional and regulatory parameters influence financial market decisions and outcomes. The researchers want to take a closer look at the interconnections between legislation, economics and politics in this area and in so doing measure and evaluate the effects of legislative proposals and amendments on the real economy. “Our objective is not only to let the two disciplines of law and economics explore a common topic but also develop joint methodologies,” explains lawyer Tobias Tröger.
The project has evolved out of the LOEWE Centre “SAFE - Sustainable Architecture for Finance in Europe” at the House of Finance of Goethe University Frankfurt. Fellows from Germany and abroad were selected beforehand who are able and willing to engage in this type of methodologically synthesising research. According to Professor Tröger, SAFE and the House of Finance already provide the infrastructure necessary for such interdisciplinary cooperation and this makes them ideal hosts for the project. Specifically, the objective is to study the market impact of legislation adopted in response to the 2007/08 financial crisis as well as investigate how certain corporate governance arrangements affect company value. Exploring the political-economy determinants of different regulatory measures is another central topic addressed by the project. Tröger is convinced: “Our results will debunk the popular myth of a ‘simple explanation’”. In addition to the spokespersons, a further six professors from Goethe University Frankfurt will engage in the project over the initial four years, together with two postdoctoral researchers, eight junior fellows and 20 fellows. The German Research Foundation has granted funding to the tune of € 3.1 million for the first four years.
The German Research Foundation is currently setting up a total of eight new Research Units, a Clinical Research Unit and two Centres for Advanced Studies, for which around € 32 million will be available in the first phase. This funding enables researchers to look at current pressing issues in their field and adopt innovative approaches in their work. In this context, the Centres for Advanced Studies are specially tailored to working practices in the humanities, meaning that they can receive funding for two four-year periods, by contrast to research groups in general, where the German Research Foundation can fund research for two three-year periods.
Portrait photographs of the spokespersons can be downloaded from: www.uni-frankfurt.de/69763182
Caption: Professor Petra Döll (photo: private), Professor Tobias Tröger (photo: IMFS/Hannelore Förster), Professor Rainer Haselmann (photo: Oli Hege)
Professor Petra Döll, Chair of Hydrology, Department of Physical Geography, Faculty of Geosciences and Geography, Riedberg Campus, Tel.: +49(0)69-798-40219, email firstname.lastname@example.org
Professor Tobias Tröger, Chair of Civil, Commercial and Business Law, Institute of Civil and Business Law, Faculty of Law, Westend Campus, Tel.: +49(0)69-798-34391, email email@example.com