An Enormous, Branching String of Galaxy Clusters Is the Largest Known Structure in the Universe, Scientists Say

Meet Quipu, a new contender for the largest known structure in the universe.

It’s essentially a giant cluster of galaxy clusters stretching approximately 1.3 billion light-years long—more than 13,000 times the length of our Milky Way. It consists of 200 quadrillion solar masses. And as if that weren’t impressive enough, Quipu and four other similar structures encompass 30 percent of the galaxies, 45 percent of the galaxy clusters, 25 percent of the matter and 13 percent of the overall volume of the known universe.

These five superstructures were described in a preprint paper published on the server arXiv last week. The paper has been accepted for publication in the journal Astronomy and Astrophysics.

“The Quipu superstructure, end to end, is slightly longer than the Sloan Great Wall,” J. Richard Gott III, an astrophysicist at Princeton University who did not participate in the study, tells New Scientist’s Alex Wilkins. The Sloan Great Wall is another superstructure identified in 2003 by astronomers led by Gott. At the time of its discovery, it was the largest observed structure in the universe. “Congratulations to them for finding it.”

The recent discovery came within the context of investigating the distribution of matter in the universe at different light wavelengths. The universe’s expansion distorts light traveling from distant objects, increasing their wavelengths and thus shifting them closer to the red part of the visible light spectrum. This phenomenon is called redshift—and the farther away an object is, the higher the redshift. The research team focused on matter within a little-studied redshift region, officially between redshift 0.03 and 0.06.

But how did they manage to “zoom out” enough to make out which cluster was part of which superstructure? Relying on data from the German ROSAT X-ray satellite, the team used a “friends-of-friends” algorithm that establishes a maximum distance between clusters for them to be considered part of the same structure, per New Scientist.

In this way, the team identified the five superstructures within a range of approximately 425 million to 815 million light-years from Earth: the Shapley supercluster, which at one time was considered the largest superstructure in the local universe; the Serpens-Corona Borealis superstructure; the Hercules supercluster; the Sculptor-Pegasus superstructure; and of course, Quipu, which researchers named after the Incan technique of recording numbers with knots on string.

In Quipu, “there is one main strand of clusters of galaxies from which many strands depart,” astrophysicist Alfredo Carpineti writes for IFL Science.

Despite being in first place, Quipu is not short on competition. At ten billion light-years long, the Hercules Corona-Borealis Great Wall is technically the largest known structure in the universe, with a catch: It hasn’t been confirmed as a single, interconnected thing, as Hans Böhringer, an astrophysicist with the Max Planck Institute for Extraterrestrial Physics and a co-author of the preprint study, tells EarthSky’s Kelly Kizer Whitt.

Böhringer, however, isn’t banking on Quipu holding the first-place spot for long, because “larger structures might (quite probably) exist if we inspect ever-larger cosmic volumes” in the more distant universe, he tells EarthSky.

Beyond the fact that its record-breaking size might soon be challenged, it’s unclear whether the matter included within Quipu is bound together by gravity, says Seshadri Nadathur, a cosmologist at the University of Portsmouth in England who was not involved in the study, to New Scientist. Hence, as the universe expands, “some of those galaxies may drift apart from each other instead of collapsing in on themselves, in which case, according to some interpretations, it’s not really a bound structure,” he adds.

Either way, in addition to the inherent excitement of getting to study the largest “things” ever, analyzing superstructures such as Quipu has practical applications for our understanding of the greater universe. For example, superstructures can bend light in a phenomenon called gravitational lensing, distort our measurements of the universe’s expansion and impact the cosmic microwave background (CMB)—a type of radiation scientists depend on to study the Big Bang.

As the cosmos evolves, Quipu and the other described superstructures might eventually pull apart “into several collapsing units,” the researchers write in the preprint. As a result, these structures are transient. “But,” the team adds, “at present they are special physical entities with characteristic properties and special cosmic environments deserving special attention.”

Margherita Bassi | READ MORE

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.