Astronomers have identified a ring-shaped arrangement of galaxies and galaxy clusters, dubbed the Big Ring, that spans about 1.3 billion light-years in diameter and sits more than 9 billion light-years from Earth. Its size matters because cosmologists calculate the theoretical upper limit for cosmic structures at roughly 1.2 billion light-years — a ceiling the Big Ring breaches. The discovery, led by University of Central Lancashire PhD student Alexia Lopez and presented at the 243rd meeting of the American Astronomical Society in New Orleans in January 2024, adds to a growing list of megastructures that appear to defy the Cosmological Principle, the assumption that matter is spread smoothly across the universe on the largest scales.
The Big Ring: A Cosmic Megastructure
The Big Ring is composed of numerous galaxies and galaxy clusters arranged in a continuous, almost perfect ring-like pattern in space, with a circumference of about 4 billion light-years. Seen from Earth, it appears roughly the size of 15 full moons placed side by side in the night sky, despite its extraordinary distance near the constellation Boötes.
Its apparent shape is not the whole story. Analysis revealed that the structure has more of a coil shape, like a corkscrew, with its face aligned with Earth — a geometry that makes it look like a ring from our vantage point. According to reporting on the discovery, there is currently no known cause for its formation within our present understanding of the universe, and it counts as the seventh large structure discovered that contradicts the expectation of smooth matter distribution across the largest scales.
How the Big Ring Was Discovered
The Big Ring was not spotted by pointing a telescope at a glowing object. It emerged from data in the Sloan Digital Sky Survey through a technique built on quasar absorption lines — a method that lets astronomers map matter too faint to see directly.
The concept works like this: quasars, the extremely bright cores of distant galaxies, shine through vast stretches of intervening space. As their light travels toward Earth, clouds of gas associated with galaxies and galaxy clusters absorb specific wavelengths, leaving dark fingerprints in the quasars' spectra. One such signature comes from doubly ionized magnesium, known as MgII absorbers. By identifying many quasars whose light shows absorption at the same distance, astronomers can reconstruct an invisible three-dimensional map of matter along that line of sight. When Lopez examined these absorption signatures in the Boötes region, the absorbers traced out the colossal ring-like pattern — a structure that would have remained hidden in a conventional galaxy survey of such distant, faint material.
