Missing baryon problem

Not to be confused with the dark matter problem or the baryon asymmetry problem.

In cosmology, the missing baryon problem is an observed discrepancy between the amount of baryonic matter detected from shortly after the Big Bang and from more recent epochs. Observations of the cosmic microwave background and Big Bang nucleosynthesis studies have set constraints on the abundance of baryons in the early universe, finding that baryonic matter accounts for approximately 4.8% of the energy contents of the Universe.[1][2] At the same time, a census of baryons in the recent observable universe has found that observed baryonic matter accounts for less than half of that amount.[3][4] This discrepancy is commonly known as the missing baryon problem. The missing baryon problem is different from the dark matter problem, which is non-baryonic in nature.[5]

  1. ^ Ade, P.A.R.; et al. (2016). "Planck 2015 results. XIII. Cosmological parameters". Astron. Astrophys. 594: A13. arXiv:1502.01589. Bibcode:2016A&A...594A..13P. doi:10.1051/0004-6361/201525830. S2CID 119262962.
  2. ^ Cooke, Ryan J.; Pettini, Max; Steidel, Charles C. (2018-03-12). "One Percent Determination of the Primordial Deuterium Abundance". The Astrophysical Journal. 855 (2): 102. arXiv:1710.11129. Bibcode:2018ApJ...855..102C. doi:10.3847/1538-4357/aaab53. ISSN 1538-4357. S2CID 56367851.
  3. ^ Henry C. Ferguson. ""The Case of the "Missing Baryons""".
  4. ^ Shull, J. Michael; Smith, Britton D.; Danforth, Charles W. (2012-11-01). "The Baryon Census in a Multiphase Intergalactic Medium: 30% of the Baryons May Still be Missing". The Astrophysical Journal. 759 (1): 23. arXiv:1112.2706. Bibcode:2012ApJ...759...23S. doi:10.1088/0004-637X/759/1/23. ISSN 0004-637X. S2CID 119295243.
  5. ^ See Lambda-CDM model. Baryons make up only ~5% of the universe, while dark matter makes up 26.8%.