On possible variation in the cosmological baryon fraction

Gilbert P. Holder, Kenneth M. Nollett, Alexander Van Engelen

Research output: Contribution to journalArticlepeer-review

41 Scopus citations


The fraction of matter that is in the form of baryons or dark matter could have spatial fluctuations in the form of baryon-dark matter isocurvature fluctuations. We use big bang nucleosynthesis calculations compared with observed light-element abundances as well as galaxy cluster gas fractions to constrain cosmological variations in the baryon fraction. Light-element abundances constrain spatial variations to be less than 26%-27%, while a sample of "relaxed" galaxy clusters shows spatial variations in gas fractions less than 8%. Larger spatial variations could cause differential screening of the primary cosmic microwave background (CMB) anisotropies, leading to asymmetries in the fluctuations, and ease some tension with the halo-star 7Li abundance. We also show that fluctuations within our allowed bounds can lead to "B-mode" CMB polarization anisotropies at a non-negligible level.

Original languageEnglish (US)
Pages (from-to)907-913
Number of pages7
JournalAstrophysical Journal
Issue number2
StatePublished - 2010
Externally publishedYes


  • Cosmological parameters
  • Cosmology: miscellaneous
  • Galaxies: abundances
  • Galaxies: clusters: general
  • Large-scale structure of universe

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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