Looking up at the night sky, what a person sees seems to be no more than points of light scattered through the dark. But pull the view back far enough, out to a scale of billions of light years, and the universe presents something that may be well beyond imagining.
In 2021 an astonishing enormous structure was discovered. It is not a giant star, nor a galaxy standing on its own, but a large-scale structure of the universe made up of great numbers of galaxies, galaxy clusters, gas and dust. Because it appears as an enormous arc, it has been given the name the Giant Arc.
Its span reaches 3.3 billion light years, and, harder still to imagine, this immense arc lies 9.2 billion light years from Earth. What human beings see today is an ancient image from an extremely distant part of the universe.
A vast alignment stretching across the universe
The name Giant Arc makes it easy to picture some enormous single celestial body. In fact it is not a planet, not a star, and not even a single galaxy. It is an enormous structure formed by the arrangement of a great deal of cosmic matter, including galaxies, galaxy clusters, gas and cosmic dust. In an extremely distant region of space this matter takes on a particular overall distribution, and the result is an arc-shaped structure 3.3 billion light years long.
How large is that scale? By way of comparison, the large-scale structures dealt with in current cosmological models come with a boundary of 1.2 billion light years, and the Giant Arc’s span of 3.3 billion light years goes far beyond that figure. That is exactly why it has attracted so much notice. It is as though an enormous curve had been drawn in the far reaches of the universe, and the length of that curve already goes well past what people ordinarily understand by the word enormous.
What lies 9.2 billion light years away?
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The Giant Arc lies 9.2 billion light years from Earth, at a redshift of 0.8. That means human beings are not seeing what the universe looks like now, but receiving extremely ancient light from very far away. The light set out from that region of the universe and travelled for a span of time hard to imagine before it arrived near Earth.
The Giant Arc is not a single unbroken line
On closer analysis, the Giant Arc can be divided into two parts. The larger is called GA-main and the smaller GA-sub. Visually the two appear to be joined to each other, but through analytical methods researchers can still tell them apart. That means the Giant Arc is not a simple, tidy, enormous curve of the kind drawn with a ruler.
It is in fact a complex structure made up of large numbers of galaxies and other cosmic matter. Standing on Earth, we may be able to picture it only as an enormous curve, but in that region of space 9.2 billion light years away it is really a vast expanse, an arrangement composed of countless celestial bodies.
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