A “giant arc” spanning 1.3 billion light years across the cosmos should not exist

A newly discovered crescent of galaxies covering 3.3 billion light–years is one of the largest known structures in the universe and challenges some of astronomers’ most basic assumptions about the cosmos.

The epic arrangement, called the Giant Arc, is made up of galaxies, galactic clusters, and a lot of gas and dust. It is located 9.2 billion light years away and spans about a fifteenth of the observable universe.

Its discovery was “fortuitous,” Alexia Lopez, a doctoral student in cosmology at the University of Central Lancashire (UCLan) in the UK, told Live Science. Lopez was assembling maps of objects in the night sky using the light of around 120,000 quasars – distant luminous nuclei of galaxies or supermassives black holes consume matter and spit out energy.

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As this light passes through matter between us and the quasars, it is absorbed by different elements, leaving telltale traces that can give researchers important information. In particular, Lopez used the marks left by magnesium to determine the distance to the intervening gas and dust, 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 intermediate material,” Lopez said.

In the midst of the cosmic maps, a structure began to emerge. “It was kind of a hint of a big arc,” Lopez said. “I remember going to Roger [Clowes] and saying ‘Oh, look at this.’ “

Clowes, his doctoral advisor at UCLan, suggested further analysis to make sure it wasn’t a random alignment or data trick. After performing two different statistical tests, the researchers determined that there was less than 0.0003% chance that the giant bow was not real. They presented their results on June 7 at the 238th Virtual Meeting of the American Astronomical Society.

But the discovery, which will take its place on the list of the greatest things in the cosmos, undermines a fundamental expectation about the universe. Astronomers have long adhered to what is called the cosmological principle, according to which, at larger scales, matter is more or less evenly distributed in space.

The Giant Arch larger than other huge assemblies, like the Great Wall of Sloan and the South Pole Wall, each of which is overshadowed by even greater cosmic features.

“There have been a number of large-scale structures discovered over the years,” Clowes told Live Science. “They are so big that you wonder if they are compatible with the cosmological principle.”

The fact that such colossal entities have clustered in particular corners of the cosmos indicates that matter may not be evenly distributed throughout the universe.

But the current Standard Model of the universe is based on the cosmological principle, Lopez added. “If we find that this is not true, maybe we need to start looking at another set of theories or rules.”

Lopez isn’t sure what these theories would look like, although she did mention the idea of ​​changing how gravity works at larger scales, a possibility that has been popular with a small but large contingent 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 dictate a theoretical limit to the size of cosmic entities.

Some research has suggested that structures should grow to a certain size and then be unable to grow larger, Pomarède told Live Science. “Instead, we keep finding these bigger and bigger structures.”

Still, he’s not quite ready to dismiss the cosmological principle, which has been used in models of the universe for about a century. “It would be very daring to say that it will be replaced by something else,” he said.

Originally posted on Live Science.