In 2021, Alexia Lopez, a British PhD student, was analyzing light from distant quasars when she made a startling discovery.
discovered a giant, nearly symmetrical arc of galaxies 9.3 billion light-years away in the constellation Boötes Shepherd. Spanning a whopping 3.3 billion light-years across, the structure spans an area 1/15th the radius of the observable universe. If we could see it from Earth, it would be the size of 35 moons projected across the sky.
known as Giant bowHulk questions some basic assumptions about the universe. According to the Standard Model of cosmology — the theory that underlies our understanding of the universe — matter should be roughly evenly distributed through space. When scientists look at the universe on very large scales, there should be no noticeable imbalances; Everything should look the same in every direction.
However, the Giant Arc is not the only example of its kind. These giant structures are now forcing scientists to re-evaluate their theory of how the universe evolved.
Lopez was studying for her master’s degree at the University of Central Lancashire in the United Kingdom when her supervisor suggested using a new method to analyze large-scale structures in the universe. It used quasars — distant galaxies that emit an extraordinary amount of light — to search for signs of ionized magnesium, a sure sign of gas clouds surrounding a galaxy. When light passes through this ionized magnesium, certain frequencies are absorbed, leaving unique optical “fingerprints” that astronomers can detect.
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“I looked at the known and documented galaxy clusters, and then began to map out what these regions looked like in The second magnesium methodLopez says. One of the groups I looked at was very small, but when I drew it in Magnesium II there was this interesting, dense band of magnesium uptake across the field of view. That’s how I ended up discovering it. It was a happy accident and I was lucky to have found him.”
Lopez’s “happy accident” revelation was startling. Looking toward the Boötes constellation, a group of 45 to 50 gaseous clouds, each associated with at least one galaxy, appears to arrange itself in an arc 3.3 billion light-years across. That’s a huge amount considering the observable universe 94 billion light years away.
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