At the HITS, I lead the research group Theoretical Astrophysics (TAP). I am also full professor at Heidelberg University and member of the faculty of the Department of Physics & Astronomy.

My group at the HITS closely collaborates with the research institutes of the Center for Astronomy at Heidelberg University (ZAH, these are ITA, ARI, LSW), as well as with the Max-Planck-Institute for Astronomy. We also participate in the Heidelberg International Max-Planck Research School (IMPRS) for Astronomy & Cosmic Physics at Heidelberg University.



  • Galaxy formation
    Galaxy formation is the central subject of my research. Here the physics involved is an incredibly complicated blend of gravity, hydrodynamics, nuclear and atomic physics, as well as magnetohydrodynamics and radiation physics. The fundamental equations governing the forces between particles and fields in this low-energy regime are all well established, yet we are far from understanding how they produce the bewildering complexity of cosmic objects we see around us, like galaxies, globular star clusters, compact objects, or damped Lyman-alpha absorbers in the intergalactic medium, to name just a few. My goal is to make progress in untangling these physical processes, to separate the important from the unimportant, and to find some answers to the many questions that astrophysicists face in contemporary extragalactic astronomy.

  • Numerical cosmology
    I make extensive use of simulation techniques to study cosmic structure formation, both based on collisionless and hydrodynamic simulations. In order to allow use of the full power of modern supercomputers, I develop massive parallel simulation algorithms for distributed memory computers, and study new methods for discretizing the Euler and Navier-Stokes equations, for example on a moving mesh. One important goal is to develop new calculational tools that allow multi-physics, multi-scale simulations on peta-scale supercomputers.

  • Dark matter and dark energy
    Through numerical N-body simulations I seek clues to the nature of the dark matter and aim at advancing strategies for exploring the formation of our Galaxy, for searching for signals from dark matter annihilation, and for designing experiments for direct detection of dark matter.  Dark energy has emerged as one of the most important challenges for modern field theory and cosmology. The evidence for an accelerated expansion history of the universe is by now quite compelling, but the magnitude of the implied dark energy component cannot be naturally explained as a vacuum energy, in addition to raising a new coincidence problem: Why is the dark energy dominating just now? I work on carrying out high-resolution cosmological simulations of different dark energy cosmologies, including also non-standard theories of gravity and coupled dark matter-dark energy cosmologies, and to compare them to the standard ΛCDM model. The goal is to explore the viability of these theories and to inform strategies for successfully constraining dark energy through observations.



The next time I teach “Fundamentals of Simulation Methods” (MVComp1) will be in the winter semester 2015/16 at Heidelberg University.



I studied physics at the University of Tübingen and the University of California at Berkeley (Diploma in Physics 1996). I obtained my PhD degree in Physics (2000) from the Ludwig-Maximilians-University in Munich, with my doctoral research carried out at the Max-Planck Institute for Astrophysics (MPA) in Garching. After a postdoc at the Harvard Center for Astrophysics in the US, I returned to MPA, where I became tenured group leader in Numerical Cosmology in 2005. In Spring 2010, I joined the faculty of Heidelberg University and became group leader at the HITS.

From 2006 to 2011, I was a member of the Young Academy at the Berlin-Brandenburg Academy of Sciences and Humanities (Berlin-Brandenburgische Akademie der Wissenschaften – BBAW) and the German Academy of Natural Scientists Leopoldina (Deutsche Akademie der Naturforscher Leopoldina). I was awarded the Otto-Hahn Medal by the Max-Planck-Society in 2000, the Heinz-Maier Leibnitz Prize of the DFG in 2004, and the Klung-Wilhelmy-Weberbank Prize for Physics in 2009. Since 2013, I am external scientific member of the Max-Planck Society at the Max-Planck Institute for Astronomy in Heidelberg.



A reasonably complete (except for some conference proceedings) list of my publications can be obtained from ADS. Most of my papers are also posted as preprints on arXiv.

You may also take a loot at the publications page of the TAP group. This also lists a number of my public outreach articles.



I have written the parallel cosmological Tree/SPH code GADGET, which is publicly available in a basic version. This code is very widely employed in cosmology by numerous research codes and has been used to carry the largest cosmological simulations thus far, with up to 300 billion particles.

I have also written a number of other codes as well, but they are only available to close collaborators. Among them are codes for parallel initial conditions generation of cosmological simulation and for the construction of equilibrium compound galaxy models. For example, I have authored the SUBFIND algorithm, both in serial and parallel versions. I have written various parallel FOF group finders, codes for constructing merger history trees, and for calculating semi-analytic galaxy formation models.

Recently, I have written the new finite-volume hydrodynamics code AREPO that is based on a moving unstructured grid that is defined as the Voronoi tessellation of a set of mesh-generating points. This allows Galilean-invariant simulations of Lagrangian nature, but at the same time retains the accurcay of traditional Eulerian approaches.