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The Biggest Thing? Supervoid Spans a Billion Light-Years

Image: Cold spot
The "cold spot" is marked by a white-bordered ellipse at the bottom right of this map of the cosmic microwave background, made using the Planck satellite. The insets show the environment of this anomalous patch of the sky - as mapped by Szapudi’s team using Pan-STARRS1 and WISE data, and as observed by Planck in the cosmic microwave background temperature data. Gergo Kranicz / ESA Planck Collaboration

Astonomers may have found "the largest individual structure ever identified by humanity," and it's ... nothing. Istvan Szapudi at the University of Hawaii and colleagues around the world have ventured a theory to explain a cosmic anomaly: A "cold spot" in heat maps of cosmic microwave background radiation has intrigued scientists since it was identified in 2004.

Szapudi's research suggests that it's a "supervoid" that measures more than a billion light years across. Variations in galaxy density and background radiation are accounted for by Big Bang physics, but this area, in the direction of the constellation Eridanus, is too vast and too empty to fit the standard variations.

Scientists Spot Largest Object in Known Universe 0:43

The void is so wide that it does funny things to light, Szapudy and his colleagues say: They suggest that light would leave the void with less energy than it had when it came in, because it was stretched out by the accelerating expansion of the universe. That could explain why the spot looks cold on radiation maps.

Even if the void is nothing, that's still something — the hole has a shape, which means it's still a structure, physically speaking. That's why Szapudi suggests it's the biggest single structure ever found. The new theory doesn't explain everything — for instance, how the void was formed, or whether other cold spots are similarly empty — but it's a potential path to understanding this enormous deep-space anomaly.

The research was published this week in the Monthly Notices of the Royal Astronomical Society.

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—Devin Coldewey