This project is continuing a very successful pioneering program in computational astrophysics centered on improving the fundamental understanding of behaviors of high-energy charged particles (also known as "Cosmic Rays") and magnetic fields in cosmic plasmas. In particular, the origins of cosmic-rays themselves and the nature of the most energetic phenomena in the universe; namely, giant radio galaxies, supernova remnants, and cosmic structures that form by gravitational collapse against the expansion of the universe. This work is based on state-of-the-art codes for compressible magnetohydrodynamics and novel schemes for following the acceleration and propagation of cosmic-rays.
These researchers have initiated the first computational study of the dynamics of radio galaxy flows that includes both the relativistic particles and the magnetic fields. These simulations revealed major flaws in standard assumptions used in this field but showed for the first time that proper simulation of the physics involved can naturally explain some major puzzles. These researchers are now carrying out three high-resolution simulations on a 600 x 200 x 200 grid. These simulations also include momentum dependence of the relativistic electrons, so they are effectively four-dimensional (plus time). A new scheme was developed to treat that important feature with great efficiency. The first large simulation of this program has already been completed.
Adam Frank, Department of Physics and Astronomy, University of Rochester, Rochester, New York
Marcia Franklin, Graduate Student Researcher
Michael Frost, Undergraduate Student Researcher
Udo Gieseler, Supercomputing Institute Research Scholar
Gianluca Gregori, Graduate Student Researcher
Byung-Il Jun, Lawrence Livermore National Laboratory, Livermore, California
Hyesung Kang, Department of Earth Science, Pusan National University, Pusan, Korea
Jongsoo Kim, Korean Astronomical Observatory, Taejon, Korea
Francesco Miniati, Graduate Student Researcher
Charles Park, Supercomputing Institute Undergraduate Intern
Lawrence Rudnick, Faculty Collaborator
Dongsu Ryu, Department of Astronomy and Space Sciences, Chungnam National University, Daejeon, Korea
Konstantin Sapogin, Graduate Student Researcher
Ian L. Tregillis, Graduate Student Researcher
99/17 |
"On the Exchange of Kinetic and Magnetic Energy Between Clouds and the Interstellar Medium," F. Miniati, T.W. Jones, and D. Ryu, The Astrophysical Journal, 517, p. 242 (1999). |
99/61 |
"3-D Simulations of the MHD Kelvin-Helmholtz Instability," T.W. Jones, D. Ryu, and A. Frank, in Numerical Astrophysics, edited by S.M. Miyama, K. Tomisaka, and T. Hanawa (Kluwer Academic Publishers, New York, 1999) p. 95. |
99/149 |
"The MHD Kelvin-Helmholtz Instability III: The Role of Sheared Magnetic Field in Planar Flows," H. Jeong, D. Ryu, T.W. Jones, and A. Frank, University of Minnesota Supercomputing Institute Research Report UMSI 99/149, September 1999. Publication in press. |
99/190 |
"Enhanced Cloud Disruption by Magnetic Field Interaction," G. Gregori, F. Miniati, D. Ryu, and T.W. Jones, University of Minnesota Supercomputing Institute Research Report UMSI 99/190, November 1999. Publication in press. |
99/224 |
"Cosmic Rays and their Radiative Processes in Numerical Cosmology," D. Ryu, F. Miniati, T.W. Jones, and H. Kang, University of Minnesota Supercomputing Institute Research Report UMSI 99/224, December 1999. Publication in press. |
99/225 |
"Ion Injection and Acceleration at Modified Shocks," U.D.J. Gieseler, T.W. Jones, and H. Kang, University of Minnesota Supercomputing Institute Research Report UMSI 99/225, December 1999. |
99/226 |
"Large Cosmic Shock Waves as Sites for Particle Acceleration," F. Miniati, D. Ryu, H. Kang, and T.W. Jones, University of Minnesota Supercomputing Institute Research Report UMSI 99/226, December 1999. |
99/227 |
"Three-Dimensional Simulations of the Parker Instability in a Uniformly-Rotating Disk," J. Kim, D. Ryu, and T.W. Jones, University of Minnesota Supercomputing Institute Research Report UMSI 99/227, December 1999. Publication in press. |
99/228 |
"Time Evolution of Cosmic-Ray Modified Plane Shocks," H. Kang and T.W. Jones, University of Minnesota Supercomputing Institute Research Report UMSI 99/228, December 1999. |
One of the key discoveries of the 20th century is the highly homologous expansion of the universe. However, within that expansion are very evident local concentrations and even collapsing structures; for example, galaxies and clusters sometimes containing thousands of galaxies. Those concentrations result from initial density perturbations in the early universe that became gravitationally unstable and energetically bound. It is now possible to carry out very high-resolution simulations of this cosmological evolution. These researchers recently discovered the existence of extensive complexes of strong shocks in cosmological simulations. Simple calculations showed that these shocks are effective sources of cosmic-rays. There are also suggestions that these cosmic-rays may even be dynamically important in cluster formation, and hence in modifying several key tests of cosmological theories.
Simulations of cosmological evolution have also been begun that will for the first time include the acceleration and propagation of cosmic-rays. The cosmic-rays scheme has been successfully ported to the cosmotology code and carried out initial low-resolution experiments. First results show some strikingly unexpected patterns between concentrations of mass, cosmic-rays, and magnetic fields. Continuing work is conducting two high-resolution simulations, examining different assumptions about the origins of cosmic magnetic fields.
A major effort is underway to develop realistic and complete models of the evolution of supernova remnants. New computations include the physics of cosmic-ray acceleration and transport using schemes pioneered at the University of Minnesota. In order to capture the particle acceleration properly in these complex flows and also the evolution of the magnetic field, very high-resolution must be used for these simulations. This project is beginning with very high resolution two-dimensional simulations on an expanding grid.
Continuing work is being done on the very successful standing program that has developed new and powerful methods for numerical simulation of collisionless plasma shocks and the acceleration there of cosmic-rays. Dr. Udo Gieseler has developed a new, efficient Monte Carlo approach to examine the microphysics at such shocks. This is giving new insights into the best ways to model the MHD turbulence that mediates particle transport in this problem. He has begun a new phase of this effort to model much more realistic, general representations of the large-scale magnetic field structures.
Further work is being done to better understand the basic problem of injection of cosmic-rays at shocks. Cosmic-rays must be injected from the thermal plasma, but the process is very complex. Finally, the first stage of the ground-breaking adaptive mesh refinement (AMR) code has been completed for cosmic-ray transport. While AMR gasdynamic codes are becoming common, the cosmic-ray problem involves diffusion, and a somewhat different approach-the problem is parabolic rather than hyperbolic.
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URL: http://www.msi.umn.edu/about/publications/annualreport/ar2000/depts/IT/PhysAstron/Astronomy/jones.html |
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