“Where Are All the Baryons in the Universe?” with Wei Cui (Tsinghua University, China)

Studies have shown that stars contain very little baryonic matter and that the majority of the baryons in the universe likely exist in gaseous form. Cool baryons are more easily observed, but what have been seen cannot account for the expected number of baryons produced in the early universe. The lack of understanding of the origin and distribution of “missing baryons” is impeding the progress in completing the picture of baryon cycling in galaxy ecosystems. The bulk of the “missing baryons” may be exist in the form of hot, extended halos around galaxies and/or filamentary structures in the cosmic web; recent observations seem to support such scenarios. However, due to the lack of a sensitive probe, the physical and chemical properties of such hot baryons are poorly measured with existing facilities, but carry critical information on the feedback processes that are deemed critical to galaxy evolution. Theory is far ahead of observation in this area; data are severely lacking. The speaker describes the missing baryon puzzle and provide a personal perspective on how to solve it.

Wei Cui is Professor at the Department of Astronomy at the Tsinghua University (China) and an American Physical Society Fellow. He obtained his PhD in physics from the University of Wisconsin-Madison in 1994, and then joined MIT as a Research Scientist, working on the construction and operation of the All-Sky Monitor (ASM) on the RXTE satellite and carrying out research on compact objects based on RXTE observations. In 2000, he joined the faculty of the Department of Physics at Purdue University, and became a full Professor in 2009. He participated in the construction and operation of VERITAS, a state-of-the-art TeV gamma-ray observatory, and re-focused his research on cosmic particle accelerators. In 2016, he accepted a joint appointment from Tsinghua University as Professor of Physics, and then joined the university fully as Professor in the newly-formed Department of Astronomy. He is the PI of the proposed Hot Universe Baryon Surveyor (HUBS) mission, which aims at filling a void in probing cosmic baryons.

Webinar was recorded on November 3, 2022