Thomas W. Jones, Fellow

Numerical Studies of Particles and Fluids in Astrophysics

These researchers continued their pioneering effort in the study of the acceleration and propagation of high-energy charged particles in cosmic plasmas, as well as some key associated astrophysical phenomena. Three large groups of magnetohydrodynamical (MHD) simulations that include innovative treatments of particle transport and other novel approaches were proposed. This group has applied their methods to the study of giant radio galaxies powered by the propagation of hypersonic plasma jets, to simulations of large-scale cosmological structure formation associated with clusters of galaxies, and to supernova remnants, the hot, chaotic bubbles formed when exploding stars blast through the diffuse interstellar medium. Since the researchers alone have the computational tools to model these phenomena in this level of physical sophistication, and since these problems are all fundamental to astrophysics, the simulations were expected to be extremely important. Each of the projects conducted by this group provides the core material for a Ph.D. thesis in progress.

One specific project performed by this research group involved simulating electron transport and synchrotron emission in radio galaxies. In this study, the researchers developed the first three-dimensional MHD radio galaxy simulations that explicitly model transport of relativistic electrons, including diffusive acceleration at shocks as well as radiative and adiabatic cooling in smooth flows. Three simulations of light Mach 8 jets, designed to explore the effects of shock acceleration and radiative aging on the non-thermal particle populations that give rise to synchrotron and inverse- Compton radiations, were investigated. Because the goal of this project was to explore the connection between the large-scale flow dynamics and the small-scale physics underlying the observed emissions from real radio galaxies, the researchers combined the magnetic field and relativistic electron momentum distribution information to compute an approximate but self-consistent synchrotron emissivity and produce detailed synthetic radio telescope observations.

Several key insights have surfaced from this approach:

• The jet head in these multidimensional simulations is an extremely complex environment. The classical jet termination shock is often absent, but motions of the jet terminus show a “shock-web complex” within the backflowing jet material of the head.
• Correct interpretation of the spectral distribution of energetic electrons in these simulations relies partly upon understanding the shock-web complex, for it can give rise to distributions that confound interpretation in terms of the standard model for radiative aging of radio galaxies.
• The magnetic field outside of the jet itself becomes very intermittent and filamentary in these simulations, yet adiabatic expansion causes most of the cocoon volume to be occupied by field strengths considerably diminished below the nominal jet value. Radiative aging is very slow in these volumes, so population aging rates vary considerably from point to point.
• Overall, the intricate dynamical behaviors in these models make it difficult to capture the histories of the non-thermal particles in broad generalizations. Understanding even the simplest of these models requires attention to details of the flow.

Research Group and Collaborators

Chang-Hyun Baek, Department of Earth Sciences, Pusan National University, Pusan, Korea
Katherine Blundell, Visiting Researcher
Litsa Close, Visiting ResearcherAdam Frank, Department of Physics and Astronomy, University of Rochester, Rochester, New York
Udo Gieseler, FG Bauphysik und Solarenergie, Universität–GH Siegen, Siegen, Germany
Gianluca Gregori, Graduate Student Researcher
Eric J. Hallman, Graduate Student Researcher
Jacob Haqq-Misra, Undergraduate Student Researcher
Hyesung Kang, Department of Earth Sciences, Pusan National University, Pusan, Korea
Jongsoo Kim, Korean Astronomical Observatory, Taejon, Korea
Francesco Miniati, Max Planck Institute for Astrophysics, Garching, Germany
Sean O’Neil, Graduate Student Researcher
Lawrence Rudnick, Faculty Collaborator
William T. Ryan, Supercomputing Institute Undergraduate Intern
Dongsu Ryu, Department of Astronomy and Space Sciences, Chungnam National University, Daejeon, Korea
Konstantin V. Sapogin, Graduate Student Researcher
Ian L. Tregellis, Graduate Student Researcher