An intergalactic ring-shaped superstructure of galaxies and galaxy clusters has been discovered – so huge it defies explanation. This is a structure that lives so deep in the universe that we see it as it was some 9.2 billion years ago.
The enormous superstructure, nicknamed the ‘Great Ring’, has a diameter of 1.3 billion light-years and a circumference of about 4 billion light-years. It is also close to another immense superstructure, the “Giant arc in the sky“, which is actually even larger at 3.3 billion light-years in diameter. The Giant Arc is located a similar distance from us in the constellation Boötes, the Herdsman. Unfortunately, these superstructures are far too faint to be seen with a backyard telescope .
In fact, both superstructures were discovered during observations conducted by Alexia Lopez with the Sloan Digital Sky Survey’s 2.5-meter telescope at Apache Point in New Mexico, USA. Interestingly, Lopez, a Ph.D. student at the University of Central Lancashire in Britain noticed the galaxies in these superstructures not because they are bright, but rather because they absorb some of the light coming from more distant galaxies. quasars. Quasars are the extremely bright interiors of active galaxies; they are powered by supermassive black holes.
“Identifying two extraordinary ultralarge structures in such a close configuration raises the possibility that together they form an even more extraordinary cosmological system,” Lopez said in a study. rack.
Related: Galaxy shapes can help identify ripples in space caused by the Big Bang
The Great Ring isn’t even a ring, really; it’s kind of curled up like a slinky. Moreover, we see it up close.
Yet the problem with the Great Ring and the Giant Arch (and other similar superstructures for that matter) is that they defy cosmological theory.
According to the theory, all structures in the universe can be traced back to what is known as the cosmic microwave background (CMB) radiation – the so-called ‘fireball of the Big bang“that scientists observe when filling the universe. For the first 300,000 years of cosmic history, the universe was a sea of compact plasma – that is, atomic nuclei and free electrons. Waves crashed through this plasma, with matter accumulating at the crests and thinning in the troughs. Scientists call these waves baryonic acoustic oscillations, or BAOs.
After those 300,000 years, however, the temperature of the universe has dropped enough to allow atomic nuclei to absorb most of their electrons and form complete atoms. You could say that the cosmic plasma ocean ‘dried up’; cosmologists call it the ‘age of recombination’. Without the electrons that constantly scattered photons, light could travel unhindered through the universe for the first time. This is what we detect as the CMB.
The CMB is littered with subtle temperature variations that correspond to areas of greater and lesser density. This is the imprint of the last acoustic waves that rippled through the plasma before the era of recombination. The crests of the waves mark what we today call the ‘cosmic web of matter’, and on these crests galaxies and clusters of galaxies began to form.
“One possibility is that the Great Ring may be related to baryonic acoustic vibrations,” says Lopez. “[These] arise from oscillations in the early universe and should appear today, at least statistically, as spherical shells in the arrangement of galaxies. However, a detailed analysis of the Great Ring showed that it is not really compatible with the BAO statement: the Great Ring is too large and not spherical.”
Cosmological theory suggests that the largest structures – in the form of chains of galaxies and clusters of galaxies – that could form BAOs should be up to 1.2 billion light-years long. Yet the circumference of the Great Ring and the length of the Giant Arc dwarf this limitation. To put into context how immense this superstructure is, the Giant Arch is one-fifteenth the radius of the entire visible universe.
There are also other enormous superstructures in the universe, such as the Sloan Great Wall, which is 1.37 billion light-years across and about a billion light-years away from us. The South Pole Wall of galaxies is a more recently discovered structure; it is 1.4 billion light years long. Then there’s the Clowes-Campusana LQG (co-discoverer Roger Clowes is also Lopez’s PhD advisor), a huge group of quasars spread over two billion light-years. We see these ancient quasars as they looked some 9.5 billion years ago.
The Laniakea Supercluster, of which the Milky Way is a part, is small by comparison, measuring just 520 million light-years across.
There are also hints of even larger structures; the “dark stream” represents the apparent motion of many galaxies in the visible universe. This movement appears to be in a preferred direction, as if something above the cosmic horizon is pulling the galaxies in one direction. However, the strength of evidence for the dark current is controversial, with some astronomers disputing its existence in general.
Nevertheless, these superstructures are so large that it is not only difficult to understand how they formed, but also difficult to decipher how they break the cosmological principle, a central tenet of the Standard Model of cosmology. This principle states that on a large scale, the distribution of matter in the universe should be uniform and that no region should look substantially different from any other region. But it is clear that the superstructure, and especially the Great Ring and the Giant Arch, stand out enormously.
“Neither of these two ultra-large structures is easily explained in our current understanding of the universe,” Lopez says. “And their ultra-large sizes, distinctive shapes and cosmological proximity must surely tell us something important – but what exactly?”
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One possibility is that the structures refer to exotic forms of currently known physics, or perhaps even to new physics. For example, the Nobel Prize winner Sir Roger Penroseprofessor emeritus at the University of Oxford, has proposed a model called Conformal cyclic cosmology to describe a cyclical universe. According to this model, evidence for gravitational waves from previous eons of the universe could manifest as giant ring-like structures in the CMB. Penrose’s model has not proven popular among cosmologists, but could the Big Ring and Giant Arc have a fighting chance?
Another possibility is that the superstructure is proof of this cosmic stringsThese are hypothetical one-dimensional defects in spacetime that are believed to have arisen during the Big Bang. Cosmic strings could potentially stretch for billions of light years, yet be narrower than the width of a proton. It has been suggested that if cosmic strings exist, they could influence the clustering of matter.
“The Great Ring and the Giant Arc, both individually and together, present us with a great cosmological mystery as we try to understand the universe and its development,” Lopez concluded.
Lopez presented the findings at the 243rd Meeting of the American Astronomical Society.