The microphysics of cosmic-ray feedback

Cosmic-rays (CRs) are relativistic particles that pervade galaxies and intergalactic space. They likely play a dynamically important role in a wide range of astrophysics systems by interacting with thermal gas via magnetic fields, whose consequence is known as CR feedback. The key to understanding CR feedback lies in how well the gas and CRs are coupled, which is in most cases described by a CR diffusion coefficient that is largely unconstrained, leading to substantial uncertainties in recent studies of galaxy formation and evolution. At microphysical level, the coupling is known to be mediated by resonant wave scattering, with waves excited by the gyro-resonant instabilities for the bulk of CR particles, yet the multi-scale nature of the problem precludes numerical studies over decades. I will describe the first effort in studying such instabilities from first principles using the novel magnetohydrodynamic-particle-in-cell technique, which precisely reproduces such instabilities and allows us to study their non-linear evolution. I will further discuss ongoing works by gradually incorporating more realistic physics, towards the long-term goal of offering faithful sub-grid models for macroscopic studies of CR feedback.

Xuening Bai (Tsinghua University)
Kohei Inayoshi
Thursday, May 27, 2021 - 4:00PM to Thursday, May 27, 2021 - 5:00PM
Prof. Xuening Bai graduated from Tsinghua University with a B.S. in mathematics and physics in 2007, and obtained his PhD in astrophysics from Princeton University in 2012. He was a Hubble Fellow and Institute for Theory and Computation (ITC) fellow at the Harvard-Smithsonian Center for Astrophysics from 2012-2017. He joined the faculty at the Institute for Advanced Study, Tsinghua University in 2017, and has been jointly appointed with Department of Astronomy since 2019. He is a theoretical and computational astrophysicist, and his research group studies protoplanetary disks and planet formation as well as several aspects of plasma astrophysics, and develops algorithms and codes for applications in these areas.