Special TAPIR Seminar

In person: 370 Cahill. To Join via Zoom: 851 0756 7442

Abstract: Cosmic rays (CRs) play a pivotal role in various astrophysical systems, delivering feedback that spans a broad range of scales. However, modeling their transport remains challenging due to the inherent multi-scale nature and microphysical complexities. Recent advancements in two-moment CR hydrodynamics have alleviated some of these challenges and deepened our understanding of CR feedback. Yet, current two-moment methods may not fully incorporate all possible CR transport processes, while the outcome of CR feedback sensitively depends on these underlying microphysics. Furthermore, numerical challenges persist, including instabilities from stiff streaming terms and ambiguities in solver design for coupled CR-MHD systems. We develop a two-moment description for CR hydrodynamics from first principles, and implement our formulation as a new CR fluid module to the ATHENA++ code. To test the code, we investigate the characteristic CR-MHD waves in such systems as benchmarks, and provide a detailed analysis of their properties. In this talk, I will introduce our formulations, and show the improved performance of our module. I will also share our preliminary findings of the CR-MHD waves. The paper has been posted on ArXiv: https://arxiv.org/abs/2509.04387.