A newly discovered crescent galaxy spanning 3.3 billion light years is one of the largest known structures in the universe and challenges some of astronomers’ most fundamental assumptions about the cosmos.
The epic arrangement, called the Giant Arc, consists of galaxies, galaxy clusters and lots of gas and dust. It is 9.2 billion light years away and spans about a 15th of the observable universe.
His discovery was “accidental,” Alexia Lopez, a PhD student in cosmology at the University of Central Lancashire (UCLan) in the UK, told Live Science. Lopez assembled maps of objects in the night sky with the light of about 120,000 quasars – distant bright cores of galaxies in which supermassive black holes consume material and spit out energy.
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When this light penetrates matter between us and the quasars, it is absorbed by various elements, leaving behind telltale traces that can provide vital information to researchers. Lopez used traces of magnesium in particular to determine the distance to the gas and dust in between, as well as the position of the material in the night sky.
In this way, the quasars “act like spotlights in a dark room, illuminating this intervening matter,” said Lopez.
A structure began to emerge in the middle of the cosmic maps. “It was kind of a hint of a great arc,” said Lopez. “I remember going to Roger [Clowes] and say, ‘Oh, look at this.’ “
Clowes, her PhD supervisor at UCLan, suggested further analysis to make sure it wasn’t a random alignment or a trick of the data. After two different statistical tests, the researchers found that the probability that the giant arch was not real was less than 0.0003%. They presented their results on June 7th at the 238th virtual meeting of the American Astronomical Society.
(Image credit: Alexia Lopez / UCLan)
But the find, which will take its place on the list of the greatest things in the cosmos, undermines a fundamental expectation of the universe. Astronomers have long adhered to the so-called cosmological principle, which states that matter is more or less evenly distributed in space on the largest scales.
The Giant Arc is larger than other giant collections, such as the Sloan Great Wall and South Pole Wall, all of which are dwarfed by even larger cosmic features.
“A number of large-scale structures have been discovered over the years,” Clowes told Live Science. “They are so big that one wonders whether they are compatible with the cosmological principle.”
The fact that such colossal beings cluster in certain corners of the cosmos indicates that material may not be evenly distributed in the universe.
But the current Standard Model of the Universe is based on the cosmological principle, Lopez added. “If we find that it is not true, we may have to start looking at other theories or rules.”
Lopez doesn’t know what these theories would look like, although she mentioned the idea of modifying the way gravity works on the largest scales, a way that has been popular with a small but noisy group of scientists in recent years.
Daniel Pomarède, a cosmographer at Paris-Saclay University in France who co-discovered the south pole wall, agreed that the cosmological principle should impose a theoretical limit on the size of cosmic units.
Some research has found that structures should reach a certain size and then can’t get any larger, Pomarède told Live Science. “Instead, we keep finding these ever larger structures.”
However, he is not quite ready to discard the cosmological principle that has been used in models of the universe for about a century. “It would be very bold to say that something else will replace it,” he said.
Originally published on Live Science.