2023RAA....23j5007Z

In the ΛCDM cosmological model, based on observations of supernovae Ia, the cosmic dark energy density is assumed to be Ω_Λ ∼ 0.70 and the gravitational mass density is assumed to be Ω_m ∼ 0.30. Based on the assumption that the observed cosmic microwave background (CMB) is a thermal relic of the early hot universe, the cosmic plasma density should be small, i.e., Ω_b ∼ 0.05 (otherwise the Sunyaev-Zeldovich effect of the cosmic plasma would ruin the observed CMB's perfect blackbody spectrum). To fill the gap between Ω_m and Ω_b, non-baryonic dark matter Ω_c ∼ 0.25 is introduced into the ΛCDM model. If the CMB is the result of a partial thermal equilibrium between cosmic radiation and cosmic plasma, then the observed perfect blackbody spectrum of the CMB can coexist with cosmic plasma. In this case, it is not necessary to introduce non-baryonic cold dark matter into cosmological models. A better candidate for dark matter is the cosmic plasma.