Figure 40: The baryon budget in the low redshift universe adopted from [421]. The census of
baryons includes the detected Warm-Hot Intergalactic Medium (WHIM), the Lyman forest, stars
in galaxies, detected cold gas in galaxies (atomic HI and molecular H2), other gas associated with
galaxies (the Circumgalactic Medium, CGM), and the Intracluster Medium (ICM) of groups and
clusters of galaxies. The sum of known baryons falls short of the density of baryons expected from
BBN: 30% are missing. These missing baryons presumably exist in some as yet undetected (i.e.,
dark) form. If a fraction of these dark baryons reside in clusters (an amount roughly comparable to
that in the ICM) it would suffice to explain the residual mass discrepancy problem MOND suffers in
galaxy clusters.
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