The cosmological principle states that at a large enough scale, the universe is uniform and isotropic. That means that it’s the same everywhere, no matter which direction you are looking at. You should not be seeing a single enormous structure in a particular direction. So imagine finding two in close proximity.
Two years ago, researchers found the Giant Arc. This is a crescent of galaxies spanning 3.3 billion light-years located 9.2 billion light-years away. Now, the same team reports the discovery of a second giant structure. They are calling it the Big Ring – it has a diameter of 1.3 billion light-years and it is also 9.2 billion light-years away. The two are only 12 degrees apart in the sky.
“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 neighbours, which is extraordinarily fascinating,” discoverer Alexia Lopez, a graduate researcher from the University of Central Lancashire, said in a statement.
“Neither of these two ultra-large structures is easy to explain in our current understanding of the universe. And their ultra-large sizes, distinctive shapes, and cosmological proximity must surely be telling us something important – but what exactly?”
An exact explanation for this is yet to be provided. According to the cosmological principle, galaxies should be evenly distributed, and despite the presence of galaxy clusters and the so-called cosmic web, these structures tend to average out. So structures cannot grow beyond a certain limit.
“Cosmologists calculate the current theoretical size limit of structures to be 1.2 billion light-years, yet both of these structures are much larger – the Giant Arc is almost three times bigger and the Big Ring’s circumference is comparable to the Giant Arc’s length,” Lopez continued.
“From current cosmological theories we didn't think structures on this scale were possible. 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 neighbours, which is extraordinarily fascinating.”
Further observations will be needed to confirm these claims and provide insight that the theory can use to understand what the presence of these structures means for our understanding of the Universe.
Lopez presented her findings on the Big Ring at the 243rd meeting of the American Astronomical Society.