The functioning of galaxies: challenges for Newtonian and Milgromian dynamics

A workshop at the University of Bonn, 23rd (Mo) - 27th (Fr) September 2019

About this workshop

One of the greatest current unsolved problems in physics is whether gravity, the least understood of the fundamental "forces", is universally Newtonian in the classical limit. Even the nature of gravitation is unclear: is it a force in the physical sense (with an exchange particle), an apparent force resulting from the distortion of space-time or just an emergent phenomenon due to entropy differences as suggested by Verlinde? Whatever the physical origin of gravitation, the empirical formulation of how a body is accelerated as a result of the mass-distribution around it can be applied to study the formation and evolution of galaxies. There are two hypothesis available for computational study now:

The hypothesis that gravitation is Newtonian, as derived empirically based on Solar-system data only, has been embedded in Einstein's interpretation of gravitation as being a geometric space-time distortion. This interpretation leads to departures from observed motions of astronomical objects when extrapolated to the scales of galaxies and beyond. These departures are usually interpreted to be due to the existence of new elementary (dark matter) particles and due to the hitherto not understood dark energy which needs to dominate the energy content of the Universe and is increasing with time.

By taking into account the new dynamics data that became available on the scales of galaxies in the late 1970s, Milgrom generalised the classical law of gravitation. The hypothesis that gravitation is Milgromian simplifies galactic astrophysics because no additional dark matter is needed and galaxies become fully self-gravitating systems based on their baryonic matter content only.

The following challenges emerge in view of the two hypotheses:

Dark matter remains elusive: There is no room for dark matter particles within the standard model of particle physics. The decades long searches in space, underground and at the Large Hadron Collider for these putative particles have all been failures, and dynamical friction on the motions of satellite and larger galaxies due to the expansive dark matter haloes is not evident, as if dark matter particles are non-existent. In addition, already early cosmological computations based on the Newtonian hypothesis with dark matter have turned up major problems (e.g. the angular momentum problem, the missing satellite problem, amongst many) which have never been solved convincingly, while new problems keep emerging (the satellite planes problem, the radial acceleration relation problem, amongst many). Can this hypothesis nevertheless be made to be consistent with the observational data?

The Milgromian hypothesis on the other hand, while accounting for many of the above problems, is a non-linear theory and thus poses computational challenges. It has, until recently and due to a variety of reasons, not been applied to the problem of galaxy formation and it is therefore unclear if galaxies will emerge to look like the observed population in this approach.

With this meeting we aim to foster a discussion between the scientists who have been studying galaxies and cosmology in these two fundamentally different hypotheses. The aim is to achieve an exchange notably also on the technical challenges in applying both hypotheses to computational astrophysics problems in view of recent advances in understanding stellar populations, which are important for quantifying feedback processes.


Please register by sending an email to with subject "registration" and let us know if you would like to give a presentation and if you do not want your name to be listed on the participants list (EU GDPR 2018). The default is that your name will be displayed. Registrations will be accepted by students at a research institution (we may need to ask for a reference letter or two) and/or researchers who have at least one peer-reviewed original research publication on a topic related to this meeting. There will be no invited or overview talks as such.
If you wish to give a talk, then please also send us a title and abstract when you register (these can be changed until the end of March). We will try our best to fulfil all requests for a talk. The proposed talks ought to be on the topic of testing Newtonian vs Milgromian gravitation and/or on technical aspects related to galaxy formation and evolution (e.g., the numerical treatment of supernova explosions, of the multiphase inter stellar medium and chemical enrichment), or on observational topics related to the Newtonian vs Milgromian gravitational problem.
The talk lengths are envisioned to be between 20 and 40 minutes, depending on how many talks are requested. There will be about 30-40 talks in total, and we are aiming to allow for ample discussion time of each presentation.
The organisers are aiming to not raise a registration fee, but financial assistance for participants will not be available.


The programme will become available here. We expect to have four sessions per day Mo to Thu, and a half-day session ending mid-Fr, with two to three talks per session.

List of participants

So far ...

  • Sambaran Banerjee, University of Bonn, Germany
  • Indranil Banik, University of Bonn, Germany
  • Michal Bilek, Observatoire Astronomique de Strasbourg, France
  • Graeme Candlish, Universidad de Valparaíso, Chile
  • Ricardo Cortes, Ciudad Universitaria, Mexico City
  • Joerg Dabringhausen, Astronomical Institute, Charles University, Prague, Czech Republic
  • Harry Desmond, Astrophysics, University of Oxford, UK
  • Antonaldo Diaferio, Universita degli Studi di Torino, Italy
  • Emilio Romano-Diaz, University of Bonn, Germany
  • Mitali Damle, University of Potsdam, Germany
  • Aaron Dutton, New York University Abu Dhabi, United Arab Emirates
  • Benoit Famaey, Observatoire Astronomique de Strasbourg, France
  • Azadeh Fattahi, Durham University, UK
  • Michael Fellhauer, Universidad de Concepcion, Chile
  • Sushmitha Dixith Ganesh, University of Bonn, Germany
  • Enrico Geraldi, University of Bonn, Germany
  • Francois Hammer, Observatorie de Paris, Paris, France
  • Michael Hilker, ESO, Garching, GermanyDragan Slavkov Hajdukovic, Institute of Physics, Astrophysics and Cosmology, Cetinje, Montenegro
  • Gerhard Hensler, University of Vienna, Austria
  • Xavier Hernandez, Ciudad Universitaria, Mexico City
  • Hosein Haghi, IASBS in Zanjan, Iran
  • Moritz Haslbauer, University of Bonn, Germany
  • Behnam Javanmardi, Obsevatorie de Paris, Paris, France
  • Prachi Khatri, University of Bonn, Germany
  • Chung-Min Ko, Institute of Astronomy, National Central University, Taiwan and Department of Physics and Center of Complex Systems, National Central University, Taiwan, R.O.C.
  • Pavel Kroupa, University of Bonn, Germany, and Charles University in Prague, Czech Republic
  • Joseph Kuruvilla, University of Bonn, Germany
  • Frederico Lelli, ESO, Garching, Germany
  • Noam Libeskind, Leibniz-Institut für Astrophysik Potsdam (AIP), Germany
  • Patrick Lieberz, University of Bonn, Germany
  • Andre Maeder, Geneva Observatory, Switzerland
  • Niels Martens, University of Bonn, Germany
  • Ricardo Adan Cortes Martin, Universidad Nacional Autonoma de Mexico
  • Stacy McGaugh, Case Western University, Cleveland, USA
  • Steffen Mieske, ESO, Santiago, Chile
  • Mordehai Milgrom, Weizmann Institute, Israel
  • Oliver Mueller, University of Strasbourg, France
  • ... MSc student from Bonn
  • Lavanya Nemani, University of Bonn, Germany
  • Wolfgang Oehm, Bonn, Germany
  • Anke Pagels-Kerp, Deutsches Zentrum für Luft- und Raumfahrt (DLR) e.V., Bonn
  • Marcel Pawlowski, AIP, Postdam, Germany
  • Charalambos Pittordis, Queen Mary University of London, UK
  • Cristiano Porciani, University of Bonn, Germany
  • Tom Richtler, Universidad de Concepcion, Chile
  • Donatella Romano, INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Italy
  • Mahmood Roshan, Dept. of Physics, Ferdowsi University of Mashhad, Iran
  • Riccardo Scarpa, Instituto de Astrofísica de Canarias, Spain
  • Earl Schulz, North Granby, CT 06060, USA
  • Jennifer Schulze, University of Bonn, Germany
  • Ashly K. Sebastine, University of Bonn, Germany
  • Constantinos Skordis, Central European Institute for Cosmology and Fundamental Physics, Prague, Czech Republic
  • Sitara Srinivasan, R N S Institute of Technology (RNSIT), Bangalore, India
  • Will Sutherland, Queen Mary University of London, UK
  • Yong Tian, Institute of Astronomy, National Central University, Taiwan, R.O.C.
  • Ingo Thies, University of Bonn, Germany
  • Guillaume Thomas, NRC Herzberg Astronomy & Astrophysics, Canada
  • Vaclav Vavrycuk, Institute of Geophysics, Czech Academy of Sciences, Prague, Czech Republic
  • Viola Vavrycukova, University of Durham, UK
  • Nils Wittenburg, University of Bonn, Germany
  • Richard P. Woodard, University of Florida, Gainsesville, USA
  • Xufen Wu, Hefej, China
  • Yanbin Yang, Paris Observatory, GEPI, France
  • Hongsheng Zhao, St. Andrews University, Scotland
  • Akram Hasani Zonoozi, University of Bonn, Germany, and IASBS in Zanjan, Iran

List of hotels

Please arrange your own travel schedule and accommodation. There are many hotels in Bonn. Within walking distance (20-30 minutes) for example:

  • Hotel Mozart
  • Intercity Hotel
  • Villa Esplanade
  • Hotel Kluth
  • Map

    The meeting will take place at the University of Bonn at the Argelander Institute of Astronomy, Auf dem Huegel 71, 53121 Bonn, with lectures in the main auditorium (Room 0.012). Please see the institute webpage for information how to travel to this location.

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  • SOC, LOC and Contact

    SOC: Indranil Banik (chair, Bonn), Hosein Haghi (Zanjan), Pavel Kroupa (co-chair, Bonn, Prague), Oliver Müller (Strasbourg), Xufen Wu (Hefei), Akram Hasani Zonoozi (Bonn, Zanjan)

    LOC: Christa Boersch, Moritz Haslbauer, Patrick Lieberz, Nils Wittenburg