Astronomers have found a colossal ring-shaped structure in the distant universe that is so large and peculiar that it challenges the standard model of cosmology. The structure, dubbed the Big Ring, has a diameter of about 1.3 billion light years and a circumference of 4 billion light years, making it one of the largest structures ever observed.
The discovery of the Big Ring, presented by Alexia Lopez, a PhD student at the University of Central Lancashire, at the 243rd meeting of the American Astronomical Society in New Orleans, contradicts a key assumption in cosmology called the cosmological principle. This principle states that on a large scale, the universe is homogeneous and isotropic, meaning that it looks roughly the same everywhere and in every direction.
However, the Big Ring is not the only structure that violates this principle. Lopez also discovered the Giant Arc, a structure spanning 3.3 billion light years, in 2021. Both structures are much larger than the theoretical size limit of 1.2 billion light years, which is the maximum size that structures could have formed through gravitational instability, the process that shapes the large-scale structure of the universe.
The Big Ring and the Giant Arc are also very close to each other in the sky, near the constellations of Boötes the Herdsman, suggesting that they might be part of a connected cosmological system. This raises the possibility that there are other ultra-large structures in the universe that have not been detected yet.
How the Big Ring was detected
The Big Ring was detected by analysing data from the Sloan Digital Sky Survey (SDSS), a catalogue of distant quasars. Quasars are extremely bright objects powered by supermassive black holes at the centres of galaxies. They act like giant, distant lamps, illuminating intervening galaxies that their light passes en route and which otherwise would go unseen.
Lopez and her colleagues used several statistical algorithms to identify potential large-scale structures and the Big Ring emerged as an almost perfect circle in the sky. However, further analysis revealed that the Big Ring has more of a corkscrew shape with its face aligned with Earth.
The Big Ring is so far away that it has taken half the universe’s life to get to us, meaning that we are seeing it as it was when the universe was about 7 billion years old. This also means that the Big Ring might have changed or disappeared by now, as the universe continues to expand and evolve.
Implications for cosmology
The existence of the Big Ring and the Giant Arc poses a serious challenge to the standard model of cosmology, which is based on the cosmological principle and the theory of inflation. Inflation is the idea that the universe underwent a brief but rapid expansion in the first fraction of a second after the Big Bang, smoothing out any initial irregularities and creating a uniform universe.
The discovery of these ultra-large structures suggests that either the cosmological principle is wrong, or the theory of inflation is incomplete, or both. Lopez said: “These oddities keep getting swept under the rug, but the more we find, we’re going to have to come face-to-face with the fact that maybe our standard model needs rethinking. As a minimum it’s incomplete. As a maximum we need a completely new theorem of cosmology.”
Lopez and her colleagues plan to continue their search for more ultra-large structures in the universe, using more data and more sophisticated methods. They hope that their findings will inspire other cosmologists to revisit the assumptions and theories that underpin our current understanding of the universe.
