Inhomogeneities in the universe

TL;DR

This paper examines galaxy distribution data, revealing inhomogeneities at scales below 100 Mpc/h, challenging standard cosmological models that assume homogeneity and isotropy at large scales.

Contribution

It introduces strategies to test assumptions in galaxy distribution analysis and provides evidence of inhomogeneity at certain scales, questioning standard cosmological predictions.

Findings

Galaxy distribution is inhomogeneous for r<100 Mpc/h.

Data shows statistical homogeneity and isotropy at larger scales.

Standard models may need revision to account for observed inhomogeneities.

Abstract

Standard models of galaxy formation predict that matter distribution is statistically homogeneous and isotropic and characterized by (i) spatial homogeneity for r<10 Mpc/h, (ii) small-amplitude structures of relatively limited size (i.e., r<100) Mpc/h and (iii) anti-correlations for r > r_c ~ 150 Mpc/h (i.e., no structures of size larger than r_c). Whether or not the observed galaxy distribution is interpreted to be compatible with these predictions depend on the a-priori assumptions encoded in the statistical methods employed to characterize the data and on the a-posteriori hypotheses made to interpret the results. We present strategies to test the most common assumptions and we find evidences that, in the available samples, galaxy distribution is spatially inhomogeneous for r<100 Mpc/h but statistically homogeneous and isotropic. We conclude that the observed inhomogeneities pose a fundamental challenge to the standard picture of cosmology but they also represent an important opportunity which may open new directions for many cosmological puzzles.