A Challenge to the Standard Cosmological Model

TL;DR

This study analyzes the sky distribution of radio galaxies and quasars to test the standard cosmological model, finding significant anisotropies that challenge the assumption of large-scale isotropy and homogeneity.

Contribution

It provides the first joint analysis of radio galaxy and quasar catalogs revealing significant dipole anisotropies inconsistent with the standard model expectations.

Findings

Both samples show dipole anisotropies with high statistical significance.

The dipoles are consistent with each other and show no frequency dependence.

Results suggest possible intrinsic anisotropy in the universe's large-scale structure.

Abstract

We present the first joint analysis of catalogs of radio galaxies and quasars to determine if their sky distribution is consistent with the standard $\Lambda$CDM model of cosmology. This model is based on the cosmological principle, which asserts that the universe is statistically isotropic and homogeneous on large scales, so the observed dipole anisotropy in the cosmic microwave background (CMB) must be attributed to our local peculiar motion. We test the null hypothesis that there is a dipole anisotropy in the sky distribution of radio galaxies and quasars consistent with the motion inferred from the CMB, as is expected for cosmologically distant sources. Our two samples, constructed respectively from the NRAO VLA Sky Survey and the Wide-field Infrared Survey Explorer, are systematically independent and have no shared objects. Using a completely general statistic that accounts for correlation between the found dipole amplitude and its directional offset from the CMB dipole, the null hypothesis is independently rejected by the radio galaxy and quasar samples with $p$-value of $8.9\times10^{-3}$ and $1.2\times10^{-5}$, respectively, corresponding to $2.6\sigma$ and $4.4\sigma$ significance. The joint significance, using sample size-weighted $Z$-scores, is $5.1\sigma$. We show that the radio galaxy and quasar dipoles are consistent with each other and find no evidence for any frequency dependence of the amplitude. The consistency of the two dipoles improves if we boost to the CMB frame assuming its dipole to be fully kinematic, suggesting that cosmologically distant radio galaxies and quasars may have an intrinsic anisotropy in this frame.