The largest structure in the observable universe or cosmic variance?


Figure 1: The coloured background indicates the peaks and troughs in the occurrence of quasars at the redshift of the Huge-LQG.  The LQG is shown as a long chain of peaks indicated by black circles. The red crosses indicate the positions of quasars in a smaller LQG, the Clowes & Campusano LQG at the same redshift, around z = 1.28. Credit: R. G. Clowes / UCLan

In late 2012 a discovery was made1 of what was afterwards called the Huge Large Quasar Group (Huge-LQG).  A collection of 73 quasars all with redshifts around a mean value of z = 1.27 was discovered in the Sloan Digital Sky Survey (SDSS DR7QSO) that covers 15 degrees across the sky.

A new discovery was made in 2013 of a massively large quasar group as indicated by the black circles in figure 1. Its longest extension is about 4 billion light-years based on standard concordance cosmology.  This was then claimed as the largest single structure in the universe. Its location on the sky is about 8.8 degrees north of the Clowes & Campusano large quasar group (LQG) at the same redshift, with a mean of z = 1.28.  The latter is indicated by the red crosses in figure 1. Continue reading