Megastructure spanning 1.3 billion light years: How the Great Ring upends cosmic models

The Great Ring, so named, is an assembly of galaxies with a diameter of approximately 1.3 billion light-years through. It stands as one of the broadest structures ever sighted in space. Situated over 9 billion light years from our planet, it's so faint that it's out of range of the unaided eye. However, if it were to be directly visible, its diameter in the night sky would coincide with that of 15 full Moons.

The sheer scale of the Great Ring appears to clash with a fundamental cosmological tenet, known as the cosmological principle. As per this principle, beyond a certain spatial expanse, the Universe is homogenous and looks identical regardless of the direction you look.

Alexia Lopez, the discoverer of the ring, expressed her amazement at the discovery in a statement to "The Guardian". "With the understanding that our current cosmological theories provide, we did not anticipate the existence of structures of this scale. We might perhaps expect to find one exceptionally large structure in our entire observable Universe," she mentioned.

The Great Ring forms part of an expanding roster of surprisingly large cosmic entities. Another is the Great Arc, neighboring the Great Ring, which Lopez also discovered in 2021.

Cosmologists have set an estimated limit to the size of cosmic structures at 1.2 billion light years. However, both the Great Ring and the Great Arc, thought to span over 3.3 billion light years, overshoot this boundary.

Both these phenomena are positioned the same distance from Earth, near the constellation Boötes, which suggests they may be part of a linked system.

"We tend to downplay these anomalies, but with an increase in such discoveries, we might have to confront the possibility that our standard model might require a revision. At the least, it appears incomplete. Perhaps we need a fresh cosmological model?" Lopez ponders.

The detection of the Great Ring was made via data analyzed from the Sloan Digital Sky Survey (SDSS), a record of far-off quasars. Their high luminosity makes them visible from billions of light years away, behaving like colossal, distant light sources, highlighting galaxies situated between them, their light making its way through these galaxies. Without the quasars, these galaxies would stay obscured.

Lopez, along with her team, utilized several statistical algorithms to spot potential large-scale structures, leading them to the Great Ring. This structure appears like an almost perfect ring in the sky. However, further studies revealed its shape to be coil-like, resembling a spiral aimed towards our planet.

The scientific community remains at odds over the mechanism that could have led to the formation of this structure. One hypothesis is a certain acoustic wave that existed in the early Universe, known as baryonic acoustic oscillations, which might have been the catalyst for spherical shells in today's galaxy system. Another explanation is the existence of cosmic strings, theoretical "flaws" in the universe's structure that could cause matter to accumulate along large-scale fault lines.

Dr. Jenny Wagner, a cosmologist associated with the Bahamas Advanced Study Institute & Conferences, described the discovery as significant. She believes it's possible to circumscribe the Great Ring within the cosmological principle, depending on how its boundaries are set. However, as the number of such mismatching large-scale structures increase, this view becomes less statistically plausible. "That's why exploring for more gigantic objects is so valuable. I personally wouldn’t be taken aback if, post future discoveries, we had to discard the cosmological principle," she said.