Cosmic megastructure discovered by graduate student challenges theories of the universe

Astronomers have discovered a ring-shaped cosmic megastructure whose proportions challenge existing theories of the universe.

The so-called Great Ring has a diameter of about 1.3 billion light years, making it one of the largest structures ever observed, writes The Guardian. More than 9 billion light-years from Earth, it is too faint to be seen directly, but its diameter in the night sky would be equivalent to 15 full moons.

The observations, presented Thursday at the 243rd meeting of the American Astronomical Society in New Orleans, are important because the size of the Great Ring appears to contradict a fundamental assumption in cosmology called the cosmological principle. He argues that above a certain spatial scale, the Universe is homogeneous and looks the same in all directions.

“Based on current cosmological theories, we didn’t think structures on this scale were possible,” said Alexia Lopes, a PhD student at the University of Central Lancashire who led the analysis. “We would expect perhaps one extremely large structure in our entire observable universe.”

Theoretically, when the scale of the Universe decreases, a vast, featureless space should open up. Yet the Great Ring is one of a growing list of unexpectedly large structures, The Guardian points out. Others include the Giant Arc, which appears right next to the Great Ring and was also discovered by Lopez in 2021. Cosmologists have calculated that the current theoretical limit on the size of the structures is 1.2 billion light-years, but the Great Ring and Giant Arc, which are estimated to span 3.3 billion light-years, violate this limit.

Interestingly, these two structures are located at the same distance from Earth, near the constellations of the Shepherd Botes, which increases the likelihood that they are part of an interconnected cosmological system, writes The Guardian.

“These oddities continue to be suppressed, but the more we learn, the more we will have to face the fact that perhaps our standard model needs to be rethought,” Lopez notes. – At a minimum, it is incomplete. At the most, we need a completely new theorem of cosmology.”

The large ring was discovered by analyzing data from the Sloan Digital Sky Survey (SDSS), a catalog of distant quasars. These objects are so bright that they can be seen from billions of light-years away, and they act like giant, distant lamps, illuminating intervening galaxies that their light passes along the way that would otherwise remain invisible.

Lopez and her colleagues used several different statistical algorithms to identify potential large-scale structures, and the Great Ring emerged. The structure appears in the sky as a nearly perfect ring, but further analysis revealed that it is shaped like a corkscrew spiral that is aligned facing Earth.

Cosmologists are not sure what mechanism could have led to the formation of this structure. One possibility is a type of acoustic waves in the early Universe known as baryon acoustic oscillations, which could have led to the formation of spherical shells in the arrangement of galaxies today. Another explanation is the existence of cosmic strings, hypothetical “flaws” in the structure of the Universe that could lead to the accumulation of matter along large-scale fault lines.

Dr Jenny Wagner, a cosmologist at the Bahamas Institute for Advanced Study and Conferences, called the discovery significant. “This doesn’t seem like a coincidence,” she said.

Wagner argues that the Great Ring can fit within the framework of the cosmological principle, depending on how its limits are defined, but the more such unusual large-scale structures are discovered, the less statistically plausible this view becomes. “That’s why finding other giant structures is so valuable,” she said. “Personally, I would not be surprised if we have to abandon the cosmological principle after future discoveries.”