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ΛCDM Graphical History

Physical CDM Density, Ωch2

By definition, ΛCDM cosmology assumes the presence of non-baryonic cold dark matter. Estimations shown in the figure are all limited to application of ΛCDM to CMB measurements. Non-CMB derived values of baryonic and total matter densities support the dark matter content found by CMB analyses (Ωc ≈ Ωm - Ωb), but don't have the tight uncertainties that current determinations using WMAP and Planck data (combined with external datasets) provide. The slight (1σ-2σ) tension between the WMAP and Planck results is consistent with the corresponding tension in Ωm and reasonably good agreement in the baryonic content values.

Universe Age 2016

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In ΛCDM, most of the Large Scale Structure in the universe is associated with cold dark matter. Dark matter is not easily detected, but its presence is inferred from gravitational effects such as lensing and galactic rotation curves. All four entries in the above plot are determined from analysis of CMB data: the current most precisely determined values are represented by the Planck 2015 and WMAP 2013 points, which also include data from other experiments. The values indicate very roughly 25% of the present-day universe is comprised of CDM; the percentage contribution from ordinary matter is much lower (see the Ωbh2 figure). Slight tension exists between WMAP and Planck CMB determinations for cold dark matter content. Unfortunately, alternate methods of corroboration at this precision level are not currently available. The gray vertical line, representing the weighted average of WMAP and Planck data points, is positioned at Ωch 2 = 0.1180.

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A service of the HEASARC and of the Astrophysics Science Division at NASA/GSFC
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