Energy dynamics in diffuse astrophysical plasmas: multiscale, multiphase, and multiphysics

• Applicant: Dr. Philipp Grete
• Subject Area: Astrophysics and Astronomy
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 555983577

Magnetic fields are observed throughout the Universe and impact the dynamics in many astrophysical systems even in cases where they are weak. This includes systems filled with diffuse, astrophysical plasmas, such as the hot gas permeating galaxy clusters or galactic atmospheres. In addition, the dynamics in these systems are impacted by multiscale processes (e.g., turbulent energy cascades), multiphase structures (e.g., cold, clumpy material moving in a hot, potentially turbulent, ambient medium), and additional physics (e.g., feedback from active galactic nuclei). Over the past decades significant progress has been made in studying these processes, both, observationally and theoretically. Nevertheless, many key questions remain unanswered particularly with respect to the detailed energy dynamics and the interplay between the multiscale, multiphase, and multiphysics processes. In this project I will address the following questions: (i) Is there an (universal) asymptotic regime in magnetohydrodynamic (MHD) turbulence, (ii) how is energy redistributed across scales and between different phases in the presence of magnetic fields, (iii) what are the observational signatures of multiphase dynamics in magnetized turbulence, and (iv) how well are idealized simulations approximating more complex multiphysics simulations and observations? While the research proposed here applies to many astrophysical systems, I will put an emphasis on galaxy clusters. To this end, I will perform (multiphase) MHD turbulence simulations with the open source, performance portable, exascale simulation code AthenaPK. Moreover, I will extend an existing energy transfer analysis framework to support multiphase plasmas. The latter will then be used to analyze simulations, including the largest MHD turbulence and isolated galaxy clusters with feedback from magnetized active galactic nuclei simulations to date. The simulations will also be post-processed for comparison with observations, e.g., in the X-ray and radio band. The major outcomes from this project will be threefold: First, the analytical results will provide a detailed description of the energy dynamics in diffuse astrophysical plasmas extending the existing description to include multiphase dynamics as well as asymptotic dynamics. Second, the comparison between synthetic and actual observations as well as between highly idealized and more realistic simulations will help determine the underlying plasma parameters by accounting for additional dynamics in the underlying models. Finally, the practical, computational aspects on performance portable code development (and its public, open source distribution) are broadly applicable and expand beyond the scope of this project – eventually lowering the threshold for other groups to leverage next generation supercomputers for their scientific applications.

• DFG Programme: Research Grants