The Challenge of the Largest Structures in the Universe to Cosmology

TL;DR

This paper demonstrates that the largest observed structures in the universe, including the Sloan Great Wall and enormous voids, are consistent with the standard LCDM cosmological model, supported by large-scale simulations.

Contribution

The study uses the Horizon Run 2 simulation to show that observed large structures are compatible with LCDM, and predicts even larger structures in future surveys.

Findings

The Sloan Great Wall is consistent with LCDM.

A larger void complex than the SGW is observed and predicted by LCDM.

Future surveys may reveal structures twice as large as the SGW.

Abstract

Large galaxy redshift surveys have long been used to constrain cosmological models and structure formation scenarios. In particular, the largest structures discovered observationally are thought to carry critical information on the amplitude of large-scale density fluctuations or homogeneity of the universe, and have often challenged the standard cosmological framework. The Sloan Great Wall (SGW) recently found in the Sloan Digital Sky Survey (SDSS) region casts doubt on the concordance cosmological model with a cosmological constant (i.e. the flat LCDM model). Here we show that the existence of the SGW is perfectly consistent with the LCDM model, a result that only our very large cosmological N-body simulation (the Horizon Run 2, HR2) could supply. In addition, we report on the discovery of a void complex in the SDSS much larger than the SGW, and show that such size of the largest void is also predicted in the LCDM paradigm. Our results demonstrate that an initially homogeneous isotropic universe with primordial Gaussian random phase density fluctuations growing in accordance with the General Relativity, can explain the richness and size of the observed large-scale structures in the SDSS. Using the HR2 simulation we predict that a future galaxy redshift survey about four times deeper or with 3 magnitude fainter limit than the SDSS should reveal a largest structure of bright galaxies about twice as big as the SGW.