Computational Astrophysics

The physics of diffuse, ionized gases - plasmas - and gravity in deep space are of great interest to researchers investigating how the early universe developed. The use of high-performance computing allows computational astrophysicists to create simulations that extend over cosmic times and distances.

Professor Tom Jones, an MSI Fellow from the Minnesota Institute for Astrophysics in the School of Physics and Astronomy (College of Science and Engineering), has used MSI’s supercomputers to investigate plasmas and gravitational fields in astrophysical environments since the 1980s. The various pioneering projects covered in this research program have formed the basis of a large number of Ph.D. theses and have resulted in many publications. In current projects, the Jones group is using powerful magnetohydrodynamics (MHD) codes on the supercomputers to create simulations that allow them to study the physical processes in diffuse gases in galaxy clusters and to investigate the outflow from massive black holes. The group has developed a high-performance MHD code called “WOMBAT,” which they are continuing to expand in order to create even high-resolution simulations and to include additional physical processes.

A 2014 paper in the Astrophysical Journal discussed a phenomenological model for thermal leakage injection in the diffusive shock acceleration (DSA) process. DSA is the acceleration that ions and electrons undergo when being repeatedly reflected and it plays an important role in astrophysical models, such as solar flares and supernova shock waves. Recently this process has been invoked to explain giant radio structures in galaxy clusters spanning several million light years. Professor Jones and his colleagues Dr. Hyesung Kang (Pusan National University, Korea), Dr. Vahe Petrosian (Stanford University, California), and Dr. Dongsu Ryu (UNIST, Korea) developed a model for injection of particles into the DSA process from kappa-like suprathermal particle populations into diffusive shock acceleration. (Kang, Hyesung, Vahe Petrosian, Dongsu Ryu, and Thomas W. Jones. 2014. Injection of kappa-like suprathermal particles into diffusive shock acceleration. Astrophysical Journal 788 (2) (JUN 20): 142.) The kappa distribution represents “thermal” population modified by resonant interactions between particles and plasma waves generated by the shock that propagate ahead of the shock. In related work, a 2013 Astrophysical Journal paper investigated nonlinear effects of wave-particle interactions on the DSA process in Type-1a-like supernova remnant blast waves. Supernova remnants are strong sources of nonthermal radiation. (Kang, Hyesung, Thomas W. Jones, and Paul P. Edmon. 2013. Nonthermal radiation from supernova remnants: Effects of magnetic field amplification and particle escape. Astrophysical Journal 777 (1) (NOV 1): 25.)

Other publications by Professor Jones during 2014 include:
• Brunetti, Gianfranco, and Thomas W. Jones. 2014. Cosmic rays in galaxy clusters and their nonthermal emission. International Journal of Modern Physics D 23 (4) (JAN 01).
• Wykes, Sarka, Huib T. Intema, Martin J. Hardcastle, Abraham Achterberg, Thomas W. Jones, Helmut Jerjen, Emanuela Orru, et al. 2014. Filaments in the southern giant lobe of Centaurus A: Constraints on nature and origin from modelling and GMRT observations. Monthly Notices of the Royal Astronomical Society 442 (4) (JAN 01): 2867-82.

Some of the largest simulations the Jones group have carried out at MSI follow the full dynamic formation of the galaxy clusters as they fall out of the expansion of the universe because of gravity. One particular study in that effort is shown in the visualizations above. The images show a snapshot in time of one cluster of galaxies formed in a simulation. The focus of this study is development of turbulent plasma flows on large scales during the collisions of clusters. A simple way to measure the strength of turbulence is to calculate the rate at which turbulent eddies spin, a measure called vorticity. In the image above, the left image shows the distribution of vorticity; the right image shows one of the physical processes that drives the generation of turbulence. From analyses like this it is possible to establish, for example, that shock waves are the principle sources for turbulence in the cluster.

posted on October 15, 2014

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