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-Introduction
-Current Members
-Previous Members
-Projects
-Quality of CFC
-Core Collapse with
  Microphysics (Extended Model Set)
-Magnetorotational Stellar Core Collapse
-Core Collapse with
  Microphysics
-Black Hole Formation
-Neutron Star Merger
-Rotating Neutron Stars
-Effective Relativistic
  Potential
-Mariage des Maillages
-Core Collapse in CFC+
-Blazar Light Curves
-Axisymmetric Core Collapse

Waveform Catalog
Gravitational waves
    from stellar core
    collapse

Literature Catalog
Gravitational waves
    from stellar core
    collapse

Many astrophysical phenomena can be simulated on computers using methods known as computational hydrodynamics. If typical velocities in the system are small and gravity is weak, it is sufficient to use the Newtonian approximation of the laws of motion and gravity.

However, in many astrophysical environments, these approximations do not hold. Supermassive black holes in quasars and solar-mass-sized black holes with accretion discs power jets made of particles which move at velocities close to the light speed. Here, special relativistic hydrodynamics is needed for numerical simulations. Our group has developed and successfully applied computer codes for such simulations of jets with various sizes and morphologies for many years.

To describe large amounts of matter compressed on small scales, one must resort to general relativity, a generalization of Newton's theory of gravity. Such a situation is encountered near black holes (the prospective driving engines of astrophysical jets), as well as in core collapse supernovae, in collapsars (one possible source of gamma-ray bursts), or in neutron stars.

Some of these scenarios are emitting gravitational radiation. While light or sound waves propagate through spacetime, gravitational waves are ripples of spacetime itself. Such spacetime distortions have been predicted by Einstein in his general theory of relativity over 80 years ago, and are planned to be measured by laser interferometers or resonant bar detectors. Such experiments (like GEO 600, LIGO, VIRGO, LISA, or IGEC) have recently started very sensitive measurements, and the first successful direct detection of gravitational waves can be envisaged within the next 5 years.

In order to accomplish a successful detection of gravitational waves, very efficient electronic filters have to be employed to extract a possible signal from the data measured by a detector. It is therefore of great importance to predict as precise as possible the signals from theoretical models of various astrophysical sources of gravitational radiation. As part of the German research network SFB Transregio 7 "Gravitational Wave Astronomy", our group takes part in this international interdisciplinary scientific effort.

Additionally, in the development of numerical codes for simulations of both special and general relativistic hydrodynamics, our group is closely collaborating 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.

	Ewald Müller	(Research group leader)
	Reiner Birkl	(PhD student)
	Nicolay J. Hammer	(PhD student)
	Thomas Mädler	(PhD student)
	Bernhard Müller	(PhD student)
	Martin Obergaulinger	(PhD student)

	Miguel A. Aloy
	(Departamento de Astronomía y Astrofísica, Universidad de Valencia, Spain)
	Harald Dimmelmeier
	(Section of Astrophysics, Astronomy & Mechanics, Aristotle University of Thessaloniki, Greece)
	José A. Font
	(Departamento de Astronomía y Astrofísica, Universidad de Valencia, Spain)
	Volker Heesen
	(Astronomisches Institut, Ruhr-Universität Bochum, Germany)
	Tobias Leismann
	Petar Mimica
	(Departamento de Astronomía y Astrofísica, Universidad de Valencia, Spain)
	Leonhard Scheck
	Florian Siebel
	(Institut für Geographie, Ludwig-Maximilians-Universität München, Germany)
	Burkhard Zink
	(Institute for Theoretical Physics, Louisiana State University, U.S.A.)

Note that the order of the projects is roughly in the order of the time of completion (oldest projects at the bottom).

• 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.

  
  

• 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 find 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, 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.

  
  

• Gravitational Waves from Black Hole Formation

  B. Zink, N. Stergioulas, I. Hawke, C.D. Ott, E. Schnetter, E. Müller

  Modeling the formation of ultracompact objects like neutron stars, quark stars, or black holes, and the gravitational radiation emitted by these catastrophic events is an intrinsically general relativistic problem. Simulating the birth of black holes requires advanced methods to solve the Einstein equations, relativistic hydrodynamics, and horizon analysis.
   

  
  

• Nonlinear Axisymmetric Pulsations of Rotating Relativistic Stars

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

  With the axisymmetric version of the "Mariage des Maillage" 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 approximated relativistic effects in simulations of supernova core collapse by using an effective relativistic potential in an otherwise standard Newtonian code. With a simple modification of the potential, such codes can be 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.

  
  

• Synthetic Light Curves of BL Lac Objects

  P. Mimica, M.A. Aloy, E. Müller, W. Brinkmann

  For the first time we have performed a two-dimensional simulation of the internal shocks in a blazar jet under realistic conditions and have computed the light curve resulting from the collision of two dense shells moving with different velocities within a jet.

  
  
  
  

• 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.