Theoretical phyiscists model the sound of gravitational waves
The idea of black holes has been around for a long time. From the original "dark stars" suggested by John Michell and Pierre Laplace 200 years ago, to ubiquitous sci-fi movies and TV series like Star Trek, the black hole (whose name was coined by John Wheeler in the 1960's) has become a familiar concept, albeit not so well understood.
And that also goes for physicists and astrophysicists working with them. Some of the strange mathematical properties of black holes, coming from Karl Schwarzschild's first solution of the Einstein field equations of general relativity in 1915, still puzzle the scientists. The existence of an event horizon and a central singularity, leading to conundrums like the information paradox, have inspired some researchers to propose alternative theories.
One of the alternative models is the gravastar (a gravitational vacuum condensate star) proposed by Pawel Mazur and Emil Mottola in 2001. A gravastar would be made of a core of exotic matter similar to dark energy, that prevents the collapse of a matter shell surrounding it, made of the normal matter that once made up a star. When the star started to collapse at the end of its life, a phase transition would happen that could create this exotic matter before the event horizon could be formed. This speculative object would be almost as compact as a black hole, but the tiny difference between them would be enough to prevent the formation of the event horizon and the conceptual questioning that comes with it.
How, then, could we tell a gravastar from a black hole? It would be almost impossible to "see" a gravastar, because of the same effect that makes a black hole "black": any light would be so deflected by the gravitational field that it would never reach us. However, where photons would fail, gravitational waves can succeed! It has long since been known that when black holes are perturbed, they "vibrate" emitting gravitational waves. Indeed, they behave as "bells", that is with a signal that progressively fades away, or "ringsdown". The tone and fading of these waves depends on the only two properties of the black hole: its mass and spin. Gravastars also emit gravitational waves when they are perturbed, but, interestingly, the tones and fading of these waves are different from those of black holes. This is a fact that was alreadyknown soon after gravastars were proposed.
After the first direct detection of gravitational waves that was announced last February by the LIGO Scientific Collaboration and made news all over the world, Luciano Rezzolla (Goethe University Frankfurt, Germany) and Cecilia Chirenti (Federal University of ABC in Santo André, Brazil) set out to test whether the observed signal could have been a gravastar or not.
When considering the strongest of the signals detected so far, i.e. GW150914, the LIGO team has shown convincingly that the signal was consistent with the a collision of two black holes that formed a bigger black hole. The last part of the signal, which is indeed the ringdown, is the fingerprint that could identify the result of the collision. "The frequencies in the ringdown are the signature of the source of gravitational waves, like different bells ring with different sound", explains Professor Chirenti.
After modelling the expected sound from a gravastar that would have the same characteristics of the final black hole, the two researchers have concluded that it would be very hard to explain the frequencies observed in the ringdown of GW150914 with a gravastar. To use the same language introduced before, although the gravitational-wave signals from gravastars are very similar to those of black holes, the tones and fadings are different. Just like two keys in a piano emit different notes, the "notes" measured with GW150914 simply do not match those that can be produced by gravastars. Hence, the signal measured cannot have been produced by two gravastars merging into another and larger gravastars. This result was recently resented in a paper published on Physical Review D.
"As a theoretical physicist I'm always open to new ideas no matter how exotic; at the same time, progress in physics takes place when theories are confronted with experiments. In this case, the idea of gravastars simply does not seem to match the observations", says Professor Rezzolla.
Cecilia Chirenti, Luciano Rezzolla: "Did GW150914 produce a rotating gravastar?", in Physical Review D 94, 084016 (2016). https://doi.org/10.1103/PhysRevD.94.084016.
Image for download: www.uni-frankfurt.de/63684192
Image caption: Gravitational wave signal from GW150914 as measured in the two detectors at Livingston and Hanford (top panel); artistic rendering of a gravastar (lower panel).
Renowned scientists from Germany and abroad discuss the location of religious topics in modern science
FRANKFURT.Professional mobility and immigration have changed society permanently, and homogenous religious landscapes in Germany belong to the past. The impact of this development on religious upbringing and education will be discussed at a conference held by the Faculty of Protestant Theology at Frankfurt's Goethe University on the 12th and 13th October 2016. All interested are welcome to attend.
In Germany, the teaching of religious studies in state schools is anchored in the constitution, and training for the required teachers takes place at universities. Until the 1960s, this was also reflected in teacher training publications, just as all other areas of education have their place in general educational science today. However, discussions about the role of religious education in modern societies have been moved out of educational and into theological faculties since Germany's student movement of 1968.
Changes in society due to increasing mobility and migratory movements also indicate a changing view of religious upbringing, education, and socialisation. The growing percentage of Muslims in the population and the request for Islamic religious studies also sheds new light on Christian religious education. However, in which field of science should the debate about this take place? Has religion been neglected in educational research until now? Or should educational research have more weight in the field of theology?
The conference "Religion and Educational Research. National Traditions and Transnational Perspectives", initiated by Prof. David Käbisch, scholar in the field of Protestant religious education, will question the significance of religion-related research in educational science, especially when compared internationally. Renowned scientists from different countries have been invited to participate, including Prof. Deirdre Raftery (Dublin, Ireland), Prof. Daniel Lindmark (Umeå, Sweden), Dr. Ezequiel Gomez Caride (Buenos Aires, Argentina), and Prof. Mette Buchardt (Aalborg, Denmark).
Against the backdrop of topical discussions about state schools as a location for Islamic religious education and the current dynamic of political conflicts in France, Turkey, the Levant, and North Africa, the conference will hear from speakers whose research projects have a special focus on Islam. Frankfurt education researcher Prof. Harry Harun Behr will speak about “Islamic Education-Research in Germany”, and Islamic studies researcher Prof. Armina Omerika will discuss "Transnationalizing the History of Islam and Islamic Education" in the case of Bosnia-Herzegovina. The main topic of the conference is one that will become more important in the future, especially in the Rhine-Main region due to its dynamic population. At the same time, it will promote the international networking of religion-related research at Frankfurt University.
Mergers expert Schweizer: Hostile takeovers are always particularly risky / Cultural differences should not be underestimated
Lars Schweizer, Professor for Strategic Management at Goethe University Frankfurt, calls the planned takeover of Monsanto by German pharmaceuticals giant Bayer a major challenge. Apart from cultural differences and the strategic repositioning of Bayer which will become necessary as a result of the takeover, Schweizer especially points out that the move originally began as a hostile takeover. “That means that so far Bayer has only been able to look at Monsanto from the outside. They know neither the exact figures nor anything about internal affairs, but instead simply made an offer on the basis of the market price.” According to Schweizer, Bayer will discover little by little whether this price is indeed justified. On average, half of all takeovers fail (see interview with Schweizer from December 2015).
With regard to cultural distance, Lars Schweizer reminds of the example of Daimler-Chrysler. “The cultural differences between Germany and the USA are not to be underestimated.” The alliance between German car manufacturer Daimler and the US-American Chrysler group in 1997, which was extolled at first as a “marriage made in heaven”, was annulled in 2007 when the targeted goals proved impossible to achieve and the value of both parts of the company dropped umpteen billion euro.
Schweizer also points out that the takeover of Monsanto will mean a shift in weights within the Bayer group and hence make strategic repositioning necessary. “Such realignment always raises the question of whether workforce and clientele will go along with it.” Monsanto’s rather poor reputation and above all its controversial glyphosate weedkiller are certainly not particularly conducive here.
Then there is the substantial purchase price which Bayer must first of all finance. Schweizer emphasizes in this context that the sum is not based on any meticulous audit, but instead ultimately on the market value of the US-American firm alone. “A takeover which originated as a hostile offer thus always involves a greater risk than mergers already are.” In Schweizer’s view, the planned takeover of Monsanto is hence a major challenge overall for the Leverkusen-based firm and only after many years will it be possible to judge accurately its success or failure.
Exhibition about Artists’ Sojourns in the Frankfurt/RhineMain Region
The Frankfurt/RhineMain region has always been characterized by the inflow and outflow of people. Many an artist has also come, spent a phase of his/her life and career here, and gone again. Taking selected figures of the mid-nineteenth to the late twentieth century as examples, the exhibition explores the reciprocal relationship between artists and their temporary home: What expectations did they come here with? What artistic potential did they bring with them? How did they contribute to the local art scene and why did they leave again?
The mobility of many artists represented a major factor in their individual networks. It was above all the prospect of sales and income opportunities that motivated artists to change locations. Relatives, friends, teachers, but also collectors and dealers informed them about the local conditions and put them in contact with people that made a stay in the Frankfurt/RhineMain regionseem advantageous. Yet the comings and goings were not always free of constraint. Particularly in the years 1933 to 1945, state terror resulted in banishment and annihilation. After the war, the renewed influx of artists from the outside helped the region reconnect with the international art world.
The art scene of the Frankfurt/RhineMain cultural region thus owes its diversity and vibrancy in no small part to the many impulses provided by migrating artists.
Comings and Goings – From Courbet to Kirkeby: Artists’ Sojourns in the Frankfurt/RhineMain Region
Exhibition at Goethe University's MUSEUM GIERSCH
September 9th 2016 - January 22nd 2017
Private guided tours in English language on request: +49(0)69 13821 – 010 (1 hour)
Fee on weekdays: 75 € (plus admission price)
Fee on Saturdays, Sundays and holidays: 80 € (plus admission price)
Schaumainkai 83 (Museumsufer)
60596 Frankfurt am Main
Gene analyses reveal that there are not one, but four giraffe species
Scientists from the Senckenberg and the Giraffe Conservation Foundation have analysed the genetic relationships of all major populations of giraffe in the wild. The large study on the genetic makeup of giraffe, published today in “Current Biology”, shows that there are four distinct giraffe species. Until now, only one giraffe species had been recognized. The unexpected results are based on analyses using several nuclear marker genes of more than 100 animals. The new insights are set to improve protection efforts of these endangered animals in Africa.
Despite their large size and iconic presence, giraffe have been incompletely explored until now, with many aspects of their biology poorly understood. Latest estimates have revealed that giraffe numbers have plummeted by >35% over the past 30 years down to approximately 100,000 individuals across their range in Africa. Traditionally giraffe are classified as one species with nine subspecies based on coat patterns, ossicone (horn) structure and geographical distribution – now, this view has to be thoroughly revised.
"We have studied the genetic relationships of all giraffe subspecies from across the continent. We found, that there are not only one, but at least four genetically highly distinct groups of giraffe, which apparently do not mate with each other in the wild. This we found looking at multiple nuclear genes considered to be representative of the entire genome" says Professor Axel Janke, researcher at the Senckenberg Biodiversity and Climate Research and Professor at the Goethe University in Frankfurt, Germany. “Consequently, giraffe should be recognized as four distinct species despite their similar appearance.”
The study and new classification is based on more than hundred skin biopsy samples from all previously recognized giraffe subspecies, which were collected by the Giraffe Conservation Foundation (GCF) and partners over the past decade including in remote areas and civil war zones. These giraffe DNA samples were then analyzed by Janke’s research group at the Senckenberg Biodiversity and Climate Research Centre in cooperation with colleagues from the Senckenberg Natural History Collections of Dresden, Germany. The sample set included for the first time the elusive Nubian giraffe, the nominate subspecies (G. c. camelopardalis) – the “camel-leopard” – described by Linnaeus in 1758 on the basis of a 200-year-old record.
The large-scale analysis of giraffe DNA also yielded further surprising insights. The formerly recognized subspecies Rothschild’s giraffe (G. c. rothschildi) turned out to be genetically identical with Nubian giraffe, and thus should be synonymized with this subspecies. Similarly, the genetic studies supported previous findings by the team that could not differentiate the formerly recognized subspecies Thornicroft’s giraffe (G. c. thornicrofti) with Masai giraffe (G. c. tippelskirchi). Additionally, research into the history of the distinct species showed that their last common ancestor lived about 0.4-2.0 million years ago, which yields a rate of speciation that is typical for mammals.
“Species conservation is based on understanding the numbers, range and threats to the species. To date, the estimated total number of all giraffe has until now not been considered a particular threat for the species’ survival. However, as we now recognize four distinct species as well as some genetically unique subspecies, some of their biodiversity is very much under threat,” explains Janke. "In particular, GCF estimates that there are maybe as few as 400 West African giraffe remaining in the wild and restricted to a small communal area in Niger. Although it is not a distinct species, this subspecies is genetically unique and requires increased special protection along with the other distinct species." Dr. Julian Fennessy, first author of the study and Co-Director of GCF adds, "Now that we know that there are four giraffe species, it is even more important and urgent to support governments and other partners across Africa to protect giraffe. We rightly worry about the fate of the African elephant, with an estimated 450,000 in the wild. By contrast, the numbers of three of the four giraffe species are rapidly declining, and two numbering <10,000 individuals in total. I think we should start working together to secure the future of giraffe in Africa and take action before it is too late.”