Astronomers have discovered what they say is the largest known structure in the universe: an incredibly big hole. The “supervoid”, as it is known, is a spherical blob 1.8 billion light years across that is distinguished by its unusual emptiness. István Szapudi, who led the work at the University of Hawaii at Manoa, described the object as possibly “the largest individual structure ever identified by humanity”.
Its existence only emerged thanks to a targeted astronomical survey, which confirmed that around 10,000 galaxies were “missing” from the part of the sky it sits in.
Szapudi’s team was intentionally searching for the void because they believed that it could explain previous observations showing that part of the sky is unusually cool.
The so-called Cold Spot was discovered 10 years ago and has proved a sticking point for the best current models for how the universe evolved following the Big Bang. Cosmological theory allows for a bit of patchiness in the background temperature, due to warmer and cooler spots of various sizes emerging in the infant universe, but areas as large and cold as the Cold Spot are unexpected.
The supervoid is not an actual vacuum, as its name suggests, but has about 20% less stuff in it than our part of the universe – or any typical region. “Supervoids are not entirely empty, they’re under-dense,” said András Kovács, a co-author at the Eötvös Loránd University in Budapest.
The structure may sound unremarkable – hardly a standalone object even – but scientists say it is unprecedented given how evenly distributed the universe normally is at this spatial scale. “This is the greatest supervoid ever discovered,” Kovács said. “In combination of size and emptiness, our supervoid is still a very rare event. We can only expect a few supervoids this big in the observable universe.”
Previously, astronomers observing in the direction of the Cold Spot had established that there was no distant void in that part of the sky, but until now the nearer sky had not been surveyed.
Even more perplexing, according to Frenk, is the fact that the supervoid can only account for about 10% of the Cold Spot’s temperature dip.
“The void itself I’m not so unhappy about. It’s like the Everest of voids – there has to be one that’s bigger than the rest,” he said. “But it doesn’t explain the whole Cold Spot, which we’re still in the dark about.”
This partial explanation could point to the existence of “exotic physics”: new weird effects that scientists don’t yet know about.