Webinar with Wei Cui (Tsinghua University, China)

Where Are All the Baryons in the Universe?

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.