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Relativistic Hydrodynamics
Gravitational Waveform Catalog

Since May 2008 I am working as an expert for safety analysis of nuclear reactors for the company AREVA NP GmbH in Erlangen, Germany. Previously, I was a Marie Curie fellow at the Section of Astrophysics, Astronomy & Mechanics of the Aristotle University of Thessaloniki in Greece. Before that I was a postdoctoral researcher in the Relativistic Hydrodynamics Group of the Max Planck Institute for Astrophysics in Garching.

Until January 2007, I was also a member of the German research network SFB Transregio 7 "Gravitational Wave Astronomy", I was a former member of the German research network SFB 375 "Astro-Particle Physics", and I was a previous informal member of the European Union Research and Training Network "Sources of Gravitational Waves".

My research interest was on relativistic hydrodynamics and numerical relativity, with particular focus on compact sources of gravitational waves, numerical methods in computational fluid dynamics, and applications of such methods in simulations of stellar gravitational collapse and rotating neutron star models. A very useful external resource on this subject is the Stellar Collapse Website.

Numerical simulations of stellar gravitational collapse are usually performed on parallel supercomputers like for instance the ones at the Garching Computing Center of the Max Planck Society, the Leibniz Computing Center of the Bavarian Academy of Sciences, or the National Computing Center of Supercomputing Applications of the University of Illinois at Urbana-Champaign.

Such simulations are based on methods also utilized in the field of acoustics, aerodynamics, combustion theory, hydrology, geology, automotive safety, and even the financing sector. For this schemes are employed which are specificly tailored for the use in astrophysics and general relativity, and for example accomodate for the fact that in a strong gravitational field spacetime is curved.

The investigated scenarios are a promising source of gravitational radiation. These distortions of spacetime are planned to be measured by laser interferometers or resonant bar detectors in the near future. Such experiments (like GEO 600, LIGO, VIRGO, LISA, or IGEC) have recently started very sensitive measurements. Many of my projects involve providing the data analysis groups of these detectors with templates of the expected waveforms, which are crucial for a successful detection of the signals.

In the development of numerical codes for simulations of general relativistic hydrodynamics (like the powerful, modern and robust three-dimensional CoCoNuT code which has been used for many projects I have been involved in), I closely collaborated with scientists from the Departamento de Astronomía y Astrofísica at the Universidad de Valencia in Spain, from the Laboratoire de l'Univers et de ses Théories at the Observatoire de Paris in France, and from the Numerical Relativity Group at the Max Planck Institute for Gravitational Physics in Potsdam, Germany.

In addition, I was the technical editor of the online journal Living Reviews in Relativity, which is a peer reviewed journal offered by the Max Planck Institute for Gravitational Physics in Potsdam. It publishes reviews of research in the theory of relativity as a free service to the scientific community. This journal is one of three journals of the Living Reviews journal family, which is hosted and supported by the Heinz Nixdorf Center for Information Management of the Max Planck Society.

This is a selection of previous and current projects pursued by me and my collaborators.

• Simulations of the Accretion-Induced Gravitational Collapse of White Dwarfs

  E.B. Abdikamalov, C.D. Ott, L. Rezzolla, L. Dessart, H. Dimmelmeier, A. Marek, H.-T. Janka

  Accretion of matter from a companion star may trigger the collapse of a white dwarf to a proto-neutron star. We have found that this process is accompanied by the emission of gravitational radiation with a particular signal structure. The signal waveform could also give information about the occurence of rotational instabilities in the nascent proto-neutron star.

  
  

• Reconstruction of Gravitational Wave Burst Signals with Bayesian Inference Techniques

  C. Röver, M.-A. Bizouard, N. Christensen, H. Dimmelmeier, I.S. Heng, R. Meyer

  The gravitational waveform burst emitted during the formation of the proto-neutron star in a stellar core collapse has a complicated structure. To be able to employ efficient filtering techniques in the search pipelines of wave detectors, we have proposed a statistical method to accurately reconstruct such waveforms using a small set of basis vectors only.

  
  

• Dynamic Migration of Rotating Neutron Stars due to a Phase Transition Instability

  H. Dimmelmeier, M. Bejger, P. Haensel, J.L. Zdunik

  In their early life, rapidly rotating neutron stars (like e.g. magnetars) can possibly encounter an instability that results in a dynamic migration to a new stable equilibrium after a collapse and a sequence of ring-down pulsations. Using fully dynamical numerical simulations, we have investigated such a scenario, where also strong gravitational waves with a complicated frequency spectrum could be emitted.

  
  

• A Solution for the Nonuniqueness Problem of the Spacetime Constraint Equations

  I. Cordero-Carrión, P. Cerdá-Durán, H. Dimmelmeier, J.L. Jaramillo, J. Novak, E. Gourgoulhon

  The otherwise very successful CFC scheme for approximating the Einstein equations in simulations of compact astrophysical objects fail at very high densities. We have found a reformulation which solves this problem and extends the applicability of CFC to e.g. black hole formation.

  
  

• Phase-Transition-Induced Collapse of a Rotating Neutron Star to a Hybrid Quark Star

  E.B. Abdikamalov, H. Dimmelmeier, L. Rezzolla, J.C. Miller

  If rotating neutron stars undergo a phase transition from regular matter to quarks in their core, the subsequent collapse can be a strong source of gravitational waves. We have performed the first-ever general relativistic simulations of this scenario, and find that resonance effects can even enhance the emission of gravitational radiation.

  
  

• Comparing Full General Relativity with the Conformally Flat Approximation in Rotating Supernova Core Collapse

  C.D. Ott, H. Dimmelmeier

  For models of rotating stellar cores collapsing to a neutron star to a with both microphysics and a simple equation of state we have demonstrated that the often used CFC approach is an excellent approximation of full general relativity.
   

  
  

• Simulations of Rotational Stellar Core Collapse in General Relativity with Microphysics (Extended Model Set)

  H. Dimmelmeier, C.D. Ott, A. Marek, H.-T. Janka

  In order to investigate the influence of various stellar progenitor models and the role of different prescriptions for the properties of matter at high densities in rotating stellar core collapse to a neutron star, we have significantly extended the parameter range in our simulations of this scenario. Again, as previously we have found a generic gravitational wave burst signal.

  
  

• Simulations of Magnetorotational Supernova Core Collapse in Newtonian and Relativistic Gravity

  M.A. Aloy, P. Cerdá-Durán, H. Dimmelmeier, J.A. Font, E. Müller, M. Obergaulinger

  Neutron stars have intense or (in the case of magnetars) even extremely strong magnetic fields. We have performed simulations which can explain what role magnetic field play during the birth of these compact objects as proto-neutron stars in a supernova core collapse event.

  
  

• Simulations of Rotational Stellar Core Collapse in General Relativity with Microphysics

  H. Dimmelmeier, C.D. Ott, H.-T. Janka, A. Marek, I. Hawke, B. Zink, E. Schnetter, and E. Müller

  We have performed the first 2D and 3D simulations of rotating stellar core collapse to a neutron star in general relativity with microphysics. We have found that the resulting gravitational wave signals are much more generic than previously anticipated.

  
  

• Nonlinear Axisymmetric Pulsations of Rotating Relativistic Stars

  H. Dimmelmeier, N. Stergioulas, J.A. Font

  With the axisymmetric version of the "Mariage des Maillages" code we have for the first time simulated pulsations in uniformly and differentially rotating neutron star models in general relativistic gravity and identified important nonlinear effects. We have also investigated the issue of detectability of gravitational wave emitted by such oscillations.

  
  

• Exploring the Relativistic Regime with Newtonian Hydrodynamics: An Improved Effective Gravitational Potential

  B. Müller, A. Marek, H. Dimmelmeier, H.-T. Janka, E. Müller, R. Buras

  We have successfully approximated relativistic effects in simulations of supernova core collapse and by using an effective relativistic potential in an otherwise standard Newtonian hydrodynamic code. With a simple modification of the gravitational potential, such codes can be easily extended into the moderately relativistic regime.

  
  

• "Mariage des Maillages":
  Combining Spectral Methods and Finite Difference Methods
  in General Relativistic Hydrodynamics

  H. Dimmelmeier, J. Novak, J.A. Font, J.M. Ibáñez, E. Müller

  Based on an axisymmetric code used for our previous simulations of general relativistic rotational core collapse we have combined spectral methods and finite difference grid methods in a 3D general relativistic hydrodynamics code.

  
  

• General Relativistic Rotational Core Collapse
  with Improved Dynamics and Waveforms in CFC+

  P. Cerdá-Durán, G. Faye, H. Dimmelmeier J.A. Font, J.M. Ibáñez,
  E. Müller, G. Schäfer

  We have improved the collapse dynamics and gravitational waveforms from the our previous simulations of general relativistic rotational core collapse by extending the mathematical approximation used in that approach to higher orders.

  
  

• Gravitational Radiation from Relativistic Rotational Core Collapse

  H. Dimmelmeier, J.A. Font, E. Müller

  We have succeeded for the first time to simulate the collapse of a rotating stellar core to a neutron star including the effects of general relativity, making a major step forward towards realistic predictions of gravitational wave signals.

  
  

Over the years, I have acquired professional experience in a number of fields, including

• computational fluid dynamics in astrophysics and nuclear engineering,
• electronic publishing,
• system administration, and
• research and development in automotive safety.

More on my expertise in these fields can be found in a detailed description.

My curriculum vitae can be downloaded in PDF format and gzipped PS format.

Here is a list of my scientific publication track record.

Here is a list of my attendance at scientific conferences and summer schools, and invited seminar talks.