A Big Ring on the Sky

TL;DR

This paper reports the discovery of a massive, circular large-scale structure called 'A Big Ring on the Sky' at redshift 0.8, using MgII-absorber catalogues, and discusses its potential cosmological implications.

Contribution

It introduces a new ultra-large structure, 'A Big Ring on the Sky', and applies multiple statistical methods to assess its significance and possible origins.

Findings

The Big Ring is approximately 400 Mpc in diameter.

The structure's significance exceeds 5 sigma compared to random expectations.

It may be related to cosmic strings or other fundamental cosmological phenomena.

Abstract

We present the discovery of `A Big Ring on the Sky' (BR), the second ultra-large large-scale structure (uLSS) found in MgII-absorber catalogues, following the previously reported Giant Arc (GA). In cosmological terms the BR is close to the GA - at the same redshift $z \sim 0.8$ and with a separation on the sky of only $\sim 12^\circ$. Two extraordinary uLSSs in such close configuration raises the possibility that together they form an even more extraordinary cosmological system. The BR is a striking circular, annulus-like, structure of diameter $\sim 400$ Mpc (proper size, present epoch). The method of discovery is as described in the GA paper, but here using the new MgII-absorber catalogues restricted to DR16Q quasars. Using the Convex Hull of Member Spheres (CHMS) algorithm, we estimate that the annulus and inner absorbers of the BR have departures from random expectations, at the density of the control field, of up to $5.2\sigma$. We present the discovery of the BR, assess its significance using the CHMS, Minimal Spanning Tree (MST), FilFinder and Cuzick & Edwards (CE) methods, show it in the context of the GA+BR system, and suggest some implications for the origins of uLSS and for our understanding of cosmology. For example, it may be that unusual geometric patterns, such as these uLSSs, have an origin in cosmic strings.