Astronomers have discovered a colossal cosmic structure that’s so big it threatens to undermine our entire understanding of the universe. The Big Ring spans about 3% of the radius of the entire observable universe – and it itself might be part of an ever bigger structure.
The Big Ring – a name that’s a hell of an understatement – is an almost perfectly circular group of galaxies and galaxy clusters with a diameter of about 1.3 billion light-years, and a circumference of around 4 billion light-years. If it was visible with the naked eye, it would be the size of 15 full Moons in the night sky.
It’s hard to overstate just how incredibly gigantic that is. Galaxy superclusters are usually the largest relatively common structure in the universe, measuring over a hundred million light-years wide. These can link up into filaments that stretch a few hundred million light-years long, forming part of the cosmic web.
Not only is the Big Ring bigger than those, but it’s bigger than should be possible for any structure to ever get. According to the Cosmological Principle, a fundamental part of physical cosmology, the universe should look uniform in all directions, for any observer anywhere within it. Sure, there are random variations in the distribution of stars and galaxies, but on the largest scales it all blends together into a homogenous pattern like static. The Cosmological Principle sets an upper limit of 1.2 billion light-years on the size of any structures – a limit that the Big Ring blatantly disregards. To continue the analogy, it would be nigh on impossible for the static on your TV to arrange itself into a big image of the Mona Lisa.
If it was a one-off find, it might be tempting to dismiss the Big Ring as an anomaly or a mistake. But it’s not the only “impossible” giant structure out there – and it’s not even the biggest. Two years ago the same astronomer, Alexia Lopez at the University of Central Lancashire, discovered a 3.3-billion-light-year-long crescent called the Giant Arc. In 2015 other scientists discovered the Giant GRB Ring, with a staggering diameter of 5.6 billion light-years. And then there’s the Hercules-Corona Borealis Great Wall, a galaxy filament that stretches an incomprehensible 10 billion light-years (although its status as a single structure is up for debate).
Stranger still, the Big Ring and the Giant Arc were discovered in the same region of sky, at around the same distance – 9.2 billion light-years from Earth. There’s a chance, the team says, that the two are actually part of a single, even larger structure.
“From current cosmological theories we didn't think structures on this scale were possible,” said Lopez. “We could expect maybe one exceedingly large structure in all our observable universe. Yet, the Big Ring and the Giant Arc are two huge structures and are even cosmological neighbors, which is extraordinarily fascinating.”
With the Cosmological Principle taking so many knocks in recent years, scientists might need to look at more outlandish models. These kinds of giant structures could be created by one-dimensional defects called cosmic strings. Or they might be a by-product of Roger Penrose’s model of Conformal Cyclic Cosmology (CCC), which basically suggests that our universe is one link in an infinite chain, where the collapse of one universe creates a Big Bang that births the next.
Astronomers will no doubt continue searching for more of these colossal structures, to help solve what amounts to the biggest mystery possible.
The research was presented at the 243rd meeting of the American Astronomical Society (AAS) on January 10.
Source: University of Central Lancashire
