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Magnetic fields in the interstellar medium (ISM) play a fundamental role in regulating star formation, guiding cosmic rays transport and acceleration, and shaping the Galactic foregrounds that limit precision in cosmology. Yet their 3D structure has remained elusive: most traditional methods measure only partial 2D information. In this talk, I will present new progress toward directly recovering the 3D geometry and strength of Galactic magnetic fields. The key idea is that turbulent gas motions leave distinct imprints on the distribution of neutral hydrogen (H I), which can be used to trace magnetic field orientation and strength in 3D. By combining modern statistical tools and machine learning with H I observations from the FAST telescope, we have constructed the first observationally anchored 3D maps of magnetic fields in diffuse interstellar clouds. These results demonstrate that mapping the full 3D magnetic field is essential for linking local interstellar turbulence to global Galactic processes. I will discuss how this new framework advances our understanding of ultra-high-energy cosmic-ray propagation and provides a foundation for more accurate modeling of Galactic foregrounds in future CMB polarization experiments.

BIO

Dr. Yue Hu is a NASA Hubble Fellow at the Institute for Advanced Study. He earned his Ph.D. in astrophysics from the University of Wisconsin–Madison. His research explores how magnetic fields and turbulence shape cosmic structures across environments ranging from the interstellar medium (ISM) and circumgalactic medium (CGM) to the intracluster medium (ICM). By combining MHD turbulence theory, large-scale numerical simulations, and machine learning, Yue reconstructs the three-dimensional structure of magnetic fields and investigates their roles in star formation, cosmic-ray transport, and multiphase gas dynamics. His work has been recognized with the Cecilia Payne-Gaposchkin Dissertation Award from the American Physical Society and the Outstanding Dissertation Award from the International Organization of Chinese Physicists and Astronomers (OCPA).

Host: Xuening Bai