The missing baryon problem is that we can't find where all of the ordinary matter that should exist is located. New studies such as this one strongly suggest that it is mostly spread diffusely between galaxies.
Fast radio bursts (FRBs) are emerging as powerful cosmological probes for constraining the baryon fraction in the intergalactic medium (IGM), offering a promising avenue to address the missing baryon problem. In this paper, we analyze constraints on the IGM baryon fraction (fIGM) using 92 localized FRBs, incorporating a corrected probability distribution function for the IGM dispersion measure within three different cosmological models. We find that variations in the underlying cosmological model have a negligible impact on the inferred values of fIGM. While the NE2001 Galactic electron density model yields slightly higher fIGM values compared to the YMW16 model, the results are consistent within the 1σ confidence level. Additionally, there is no statistically significant evidence for redshift evolution in fIGM. Our analysis constrains fIGM to the range 0.8∼0.9, providing strong support for the idea in which the majority of the missing baryons reside in the diffuse IGM.
Yang Liu, Yuchen Zhang, Hongwei Yu, Puxun Wu, "Constraining the Baryon Fraction in the Intergalactic Medium with 92 localized Fast Radio Bursts" arXiv:2506.03536 (June 4, 2025).
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