The Hercules–Corona Borealis Great Wall (HCB)[1][5] or simply the Great Wall[6] is a galaxy filament that is the largest known structure in the observable universe, measuring approximately 10 billion light-years in length (the observable universe is about 93 billion light-years in diameter).

This massive superstructure is a region of the sky seen in the data set mapping of gamma-ray bursts (GRBs) that has been found to have a concentration of similarly distanced GRBs that is unusually higher than the expected average distribution.

[2][3] It was discovered in early November 2013 by a team of American and Hungarian astronomers led by István Horváth, Jon Hakkila and Zsolt Bagoly while analyzing data from the Swift Gamma-Ray Burst Mission, together with other data from ground-based telescopes.

[10][11] A 2020 paper (by the original group of discoverers and others) says that their analysis of the most reliable current dataset supports the structure's existence, but that the THESEUS satellite will be needed to decide the question conclusively.

The nomenclature was used by Jacqueline Howard, on her "Talk Nerdy to Me" video series,[17] and Hakkila would later use the name.

[1] The term is misleading, since the clustering occupies a region much larger than the constellations Hercules and Corona Borealis.

[6] The paper states that "14 of the 31 GRBs are concentrated within 45 degrees of the sky",[3] which translates to the size of about 10 billion light-years (3 gigaparsecs) in its longest dimension,[original research?]

Since the sky distribution of any object is composed of two orthogonal angular coordinates, the team used this methodology.

The team also used a bootstrapping statistic to determine the number of GRBs within a preferred angular area of the sky.

The test showed that the 15–25% of the sky identified for group 4 contains significantly more GRBs than similar circles at other GRB redshifts.

The team built statistics for this test by repeating the process a large number of times (ten thousand).

From the ten thousand Monte Carlo runs they selected the largest number of bursts found within the angular circle.

A study in 2016 found that the observed distribution of GRBs was consistent with what could be derived from Monte Carlo simulations, but was below the 95% probability threshold (p < .05) of significance typically used in p-value analyses.

[10] A 2020 paper (by the original group of discoverers and others) says that their analysis of the most reliable current dataset supports the structure's existence, but that the THESEUS satellite will be needed to decide the question conclusively.