Constraints on Cosmologically Coupled Black Holes from Planck 2018 and Other Cosmological Probes

Abstract: Cosmologically coupled black holes (CCBHs) are alternative black hole models whose masses evolve as $M \propto a^3$ on cosmological scales. This characteristic suggests that CCBHs could contribute to the accelerated expansion of the Universe. In this paper, I consider a CCBH model in which the cosmological constant is effectively induced, while the baryonic mass is conserved within conventional black holes. This model is motivated by the theoretical framework of Schwarzschild - de Sitter black holes. Assuming that the accelerated cosmic expansion is caused by CCBHs, I perform a cosmological parameter estimation using datasets including Planck 2018 CMB, CMB lensing, BAO, and supernovae. The analysis reveals notable shifts in cosmological parameters, such as $H_0 = 72.24^{+0.34}_{-0.35} \mathrm{km/s/Mpc}$, compared to the standard $\Lambda \mathrm{CDM}$. My $H_0$ constraint is consistent with the value $H_0 = 73.04 \pm 1.04 \mathrm{km/s/Mpc}$ reported by SH0ES within $1 \sigma$. However, the overall fit to the data worsens, with a total $\chi^2 = 2884.12$ for the CCBH model, compared to $\chi^2 = 2836.12$ for the $\Lambda$CDM model. I show that the effect of cosmological coupling is suppressed by a factor of $10^{-16}$ at $\sim$pc scales, rendering it negligible compared to the standard black hole mass in local astrophysical phenomena, although the CCBH model can explain the accelerated expansion.