The Hercules-Corona Borealis Great Wall

The Hercules - Corona Borealis Great Wall (HCBGW) is the largest known structure in the observable universe. It is a massive filament of galaxies; essentially a “supercluster of superclusters” that stretches across a staggering portion of the cosmos in the constellations Hercules, Corona Borealis, Lyra, Boötes, and Draco, covering a vast region of the northern sky. Its discovery and immense size have profound implications for our understanding of cosmic structure and the evolution of the universe.
 
Astronomers first detected the Hercules–Corona Borealis Great Wall in November 2013 while analyzing the distribution of gamma-ray bursts (GRBs) across the universe. A team led by István Horváth, Jon Hakkila, and Zsolt Bagoly used data from the Swift Gamma-Ray Burst Mission, supplemented with observations from ground-based telescopes, to map where GRBs were occurring. GRBs are extremely luminous explosions from distant, massive stars and are rare, making them effective tracers of large-scale cosmic structures. During their analysis, the astronomers noticed an unusual concentration of GRBs in a specific region of the sky, particularly in the direction of the constellations Hercules and Corona Borealis. This clustering suggested the presence of a massive structure, as GRBs are associated with regions containing large amounts of matter and active star formation.
 
Recent analyses suggest the HCBGW may extend up to 15 billion light - years, significantly larger than the original estimate of 10 billion light - years, with its width approximately 7.2 billion light - years. Its thickness is estimated to be nearly 1 billion light - years. The HCBGW redshift range is roughly 1.6 to 2.1, corresponding to about 10 billion light - years from Earth, with a present co-moving distance of 15 - 17.7 billion light - years. For perspective, the Milky Way galaxy is about 100,000 light - years across, and our home supercluster (Laniakea) is about 500 million light - years wide; both are dwarfed by the HCBGW. It is large enough to fit over 94,000 Milky Way galaxies placed side by side along the Great Wall’s longest side.
 
The sheer size of the HCBGW challenges current cosmological models, which predict an upper limit to the size of structures that can form in the universe due to inflationary theory and the “cosmological principle” (the idea that the universe is homogeneous and isotropic on large scales). Some researchers have questioned the reality of the structure, suggesting that statistical biases or incomplete data might explain the observed clustering of GRBs. However, more recent studies with larger GRB samples have continued to support its existence, though uncertainties remain. The latest research indicates the structure is even larger and possibly closer to Earth than previously thought, but the full extent is still undetermined due to observational limitations.
 
The existence and true size of the HCBGW remain active topics of research. More comprehensive GRB surveys and future missions (such as the THESEUS satellite) are expected to provide better data to confirm the structure’s boundaries and nature. The discovery underscores the scale and complexity of cosmic structures and may prompt revisions to standard cosmological models if confirmed beyond doubt.
 
References
(2025, March 19). Hercules - Corona Borealis Great Wall. In Wikipedia. https://en.wikipedia.org/wiki/Hercules%E2%80%93Corona_Borealis_Great_Wall

Deeks, R. (2024, August 1). The biggest thing in the Universe is the Hercules-Corona Borealis Great Wall, measuring 10 billion lightyears across. BBC Sky at Night Magazine. https://www.skyatnightmagazine.com/space-science/hercules-corona-borealis-great-wall

Horvath, I., Bagoly, Z., Hakkila, J. & Toth, L.V. (2014, August 18). New Data Support the Existence of the Hercules-Corona Borealis Great Wall. Astronomy & Astrophysics. https://www.aanda.org/articles/aa/full_htm/2015/12/aa24829-14/aa24829-14.html