THE BIG RING BY NUMBERS

light years from Earth It has a diameter of

light years

It has a circumference of

light years You’d need

full Moons to cover it It’s one of two large structures near the constellation of Boötes

They are

degrees apart

It’s the seventh large structure challenging the cosmological

principle observable space as was once thought. What’s more, it would seem that these structures are becoming less and less rare.

In January 2024, Lopez announced her second major discovery: another whopping cosmic megastructure made up of galaxies and galaxy clusters, this time presenting itself as an almost-circular ring. As it happens, this so-called ‘Big Ring on the Sky’ is also in the constellation of Boötes, with both of Lopez’s discoveries at exactly the same cosmological redshift and separated in the sky by just 12 degrees. The Big Ring’s stats are impressive. More than 9 billion light years away, it has a diameter of about 1.3 billion light years and a circumference of 4.1 billion light years. There is also a chance that it’s in the same connected cosmological system as the Giant Arc, but even taking it on its own, it’s so large that if you were to observe it from Earth it would be like seeing the equivalent of 15 full Moons. “From current cosmological theories, we didn’t think structures on this scale were possible,” Lopez says about the discovery. “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.”

The Big Ring was found in the exact same way as the Giant Arc – by observing the magnesium II absorption lines in the spectra of quasars. Since the quasars are so bright, they effectively shed light on the intervening galaxies and clusters. It’s then possible to get a sense of the overall structure through a painstaking, timeconsuming process that consumes a vast amount of computing power. This isn’t an observation which could be made with the naked eye. “A quasar acts like a giant lamp shining a spotlight through other galaxies, with the light eventually reaching us here on Earth,”

This axonometric visualisation gives you an idea of the Sloan Great Wall, which measures

1.37 billion light years in length

Lopez is a

PhD student in cosmology and astrophysics at the University of Central Lancashire and has now made two giant structure discoveries

Lopez says, explaining the process. “We can use telescopes to measure the spectra of these quasars, which essentially tells us the journey that the quasar light has been through, and in particular where the light has been absorbed. We can locate where the quasar light has passed through galaxies by a signature magnesium II doublet feature, which is a distinctive pair of absorption lines in the spectra. From this easily identified absorption ‘fingerprint’, we can map low-luminosity matter that would usually go unseen due to its faint light emitted in comparison to the quasars.”

Lopez has sought to learn more about the Big Ring, which isn’t quite as ring-like as she first thought it to be. Instead, she says it takes the form of a coil, making it more like a corkscrew. Aligned face-on with our planet, it existed when the universe was half its present age. “This data we’re looking at is so far away that it has taken half the universe’s life to get to us, so from a time when the universe was about 1.8 times smaller than it is now,” Lopez explains. “The Big Ring and the Giant Arc, both individually and together, give us a big cosmological mystery as we work to understand the universe and its development.”

Work is now taking place to try and figure out how these ultra-large structures could have formed. “Neither of these two ultra-large structures is easy to explain in our current understanding of the universe,” Lopez says. “And their ultra-large sizes, distinctive shapes, and cosmological proximity must surely be telling us something important… but what exactly?” Lopez suggests that the Big

Ring could be related to baryon acoustic oscillations (BAOs). These sound waves arose in the early universe, soon after the Big Bang, when particles began to be pulled together by gravity, making a faint imprint on matter and influencing galaxy