Matthias Liebendoerfer

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Research Summary

[ High Energy Astrophysics, Computational Astrophysics ]

Matthias Liebendoerfer is interested in the physics of supernova explosions. He is working on accurate neutrino transport in spherically symmetric supernova models and in preparing efficient approximative numerical methods for the time after the physical reasons for supernova explosions have become more evident. Predictions of the neutrino signal and the supernova nucleosynthesis will tie possible observations to the deepest layers of the supernova event. His research interests in antenna design and the propagation of electromagnetic waves in buildings are currently on hold.

Research Projects:
(September 2002 - August 2003)

General relativistic supernova code

M. Liebendoerfer has completed the world's first detailed documentation of a general relativistic supernova code with Boltzmann neutrino transport. Accurate neutrino transport is essential to quantify the energy deposition of outstreaming neutrinos behind the stalled shock. It is still not known how the shock is revived to produce a supernova explosion. M. Liebendoerfer has parallelized parts of the code with OMP and adapted it to the SMP machines at CITA. New tools for the detailed analysis of the calculated neutrino signal have been developed.

Comparison of numerical methods

M. Liebendoerfer, M. Rampp (Max-Planck Institute for Astrophysics, Garching, MPA), H.-T. Janka (MPA), and A. Mezzacappa (Oak Ridge National Laboratory, ORNL) have compared in detail their supernova simulations implementing an implicit solution of the Boltzmann transport equation or a variable Eddington factor method for the neutrino transport and found satisfactory agreement in spherical symmetry.

Investigation of electron capture rates

In collaboration with K. Langanke (Univ. of Aarhus), G. Martinez-Pinedo (Institut d'Estudis Espacials de Cataluny, Barcelona, IEEC), J. M. Sampaio (Univ. of Aarhus), D. J. Dean (ORNL), W. R. Hix (University of Tennessee, Knoxville, UTK), O. E. B. Messer (UTK), A. Mezzacappa (ORNL), H.-T. Janka (MPA), and M. Rampp (MPA), Liebendoerfer investigated the electron capture rates on heavy nuclei. They found that Pauli blocking does not occur to the extent assumed in previous core collapse simulations. Simulations with the improved rates showed that these ignored reactions actually dominate throughout core collapse. As electron capture rates and neutrino transport during stellar core collapse determine the degree of deleptonization of the inner core, these findings might have important consequences for the onset of a supernova explosion.

Singularity excision algorithm

With D. Richmond (Univ. of Victoria), M. Liebendoerfer has supplemented the adaptive grid in the hydrodynamics code AGILE with a singularity excision algorithm to be combined with neutrino transport in future predictions of the neutrino signal after a failed supernova explosion.

Impact of weak interactions

P. Hauser (Univ. of Basel), G. Martinez-Pinedo (IEEC), M. Liebendoerfer, W. R. Hix (UTK), and F.-K. Thielemann (Univ. of Basel) investigated the impact of weak interactions in the vicinity of the mass cut in nucleosynthesis calculations for supernova explosions. Previous calculations assumed an unchanged progenitor composition. It turns out that the large neutrino fluxes drive the electron fraction to higher values, sometimes even above Ye=0.5. As the data from observational analysis of supernova ejecta on metal-poor stars accumulate, a new generation of supernova nucleosynthesis calculations may shed new light on the conditions during the supernova explosion.

Neutron star merger

S. Rosswog (Univ. of Leicester) and M. Liebendoerfer carried out a three-dimensional simulation of a neutron star merger with a realistic equation of state and a new neutrino leakage scheme. A high resolution smoothed particle hydrodynamics method was used for this second merger calculation that includes neutrino physics. The common features and differences in the neutrino signal with respect to the signal from a supernova have been worked out.

Parallel code development

M. Liebendoerfer has created a new and concise implementation of cubic domain decomposition with MPI for distributed memory computations in the three-dimensional MHD code developed by Ue-Li Pen, Phil Arras, and ShingKwong Wong. A concise and fast code facilitates student projects and the extension with input physics. The Lattimer-Swesty equation of state has been tabulated for future multidimensional magneto-hydrodynamics simulations in the supernova context.

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