MigL Posted September 12, 2020 Share Posted September 12, 2020 Apparently Dark Matter is 'darker' than previously thought. It seems that the gravitational lensing produced by Dark Matter distributions in certain galaxy clusters is up to 10x greater than expected from galactic rotations and orbits ( motions ). Indcating that not only are we in the 'dark' as to its make-up, but also distributions and/or properties. https://www.msn.com/en-ca/weather/topstories/astronomers-discover-a-surprise-twist-in-the-mystery-of-dark-matter/ar-BB18Wylr?ocid=msedgntp Link to comment Share on other sites More sharing options...
drumbo Posted September 12, 2020 Share Posted September 12, 2020 Quote The light shines in the darkness, and the darkness has not overcome it. John 1:5 Link to comment Share on other sites More sharing options...
LaurieAG Posted September 12, 2020 Share Posted September 12, 2020 4 hours ago, MigL said: Indicating that not only are we in the 'dark' as to its make-up, but also distributions and/or properties. It's probably just due to the critical overdensity constant, Δc, being used for the dm halo. https://en.wikipedia.org/wiki/Virial_mass#Virial_radius This definition is not universal, however, as the exact value of Δc depends on the cosmology. In an Einstein–de Sitter model, it is assumed that the density parameter is due to matter only, where Ωm = 1. Compare this to the currently accepted cosmological model for the Universe, ΛCDM model, where Ωm = 0.3 and ΩΛ = 0.7; in this case, Δc ≈ 100 (at a redshift of zero; the value approaches the Einstein-de Sitter value with increased redshift). Nevertheless, it is typically assumed that Δc = 200 for the purpose of using a common definition, and this is denoted as r200 for the virial radius and M200 for the virial mass. The Milky Way's dm halo radius is approximately 10 times the baryonic matter radius (according to Wikipedia) so the dm volume is approximately 1000 times that of the baryonic matter volume (1^3 vs 10^3). If we keep the dm to baryonic matter ratio the same, as that derived with the ΛCDM model from the PLANCK data, we get a critical dm overdensity in the Milky Way that is half the average dm overdensity (i.e. 200 in 1000 times the baryonic matter volume) compared with ΛCDM (i.e. 100 in only 500 times the baryonic matter volume) Spoiler This makes me wonder if the Δc used in the ΛCDM model is the CMBR Δc in the past and not the local galactic Δc being measured now. Link to comment Share on other sites More sharing options...
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