Giant arc shakes up cosmology

No matter how we point our telescopes, the universe looks pretty much the same, and if we go far enough, galaxies are evenly distributed all over the place. Our knowledge of the universe is based on this assumption, so when British astronomy student Alexia Lopez saw a narrow strip of galaxies running from east to west in an image of the sky, she was surprised. The universe seemed to be smiling at her.

As a student at the University of Central Lancashire in the UK, Alexia Lopez looked for patterns in the distribution of galaxies billions of light years from Earth. And when she zoomed out and looked at a larger patch of sky, she was no longer surprised – only completely stunned.

I found an absurdly large, almost symmetrical arc of galaxies spanning 3.3 billion light-years – one of the largest structures ever discovered in the universe. giant bow It is about 9.2 billion light-years away, and if we could see it with the naked eye, it would stretch across the sky like 20 full moons in a row.

discovery It’s remarkable because such large structures go against the cosmological theory of the structure of the universe, which states that each piece of the universe appears to be a different part.

So the laughing arc is so huge that it shouldn’t even exist, and it tests the physical theory of the evolution of the universe – perhaps the universe isn’t as old as we thought after all.

The matter must be unified

For more than 100 years, astronomers have built on the assumption that the universe is homogeneous and isotropic. This means that matter is evenly distributed over a wide range and that the universe appears the same in all directions.

It seems strange that physicists assume that the universe is a uniform mass. After all, we see that this is not so – just look at ourselves.

As humans, we are denser than the air around us, and in our patch of universe matter has accumulated in a rocky planet surrounded by emptiness. It orbits another high-density spherical object, the Sun.

The solar system is part of a galaxy, one of billions of star groups in the universe, so it doesn’t exactly look as if matter is evenly distributed throughout the universe.

However, the cosmological principle states that matter in one part of the universe is no more dense than in another part of the universe. If you zoom out, the matter will be evenly distributed and will not be grouped together.

Physics simplifies the universe

our system, Milky WayIt contains 100 to 400 billion stars, many of which have planets. The Milky Way is just one of a trillion galaxies in the visible universe. Galaxies orbit each other in clusters, which in turn can be grouped into giant clusters.

According to the cosmological principle, there can be large galaxy clusters, but if matter is evenly distributed, there is a limit to how wide the structures can be. Advanced Mathematics Sets the Limit 1.2 billion light years, or 11,000 billion billion kilometres. And the giant bow discovered by Alexia Lopez is almost three times larger.

But if the cosmological principle is not proven, then we have to reconsider the cosmological standard model itself, which is based on Einstein’s 1915 general theory of relativity.

The theory of relativity tells us that we can think of gravity as the curvature of spacetime caused by the matter – or, more generally, energy – in the universe.

Einstein’s equations are difficult to apply, but in the 1920s and 1930s physicists Alexander Friedman, Georges Lemaitre, Howard B. Robertson, and Arthur J. Walker used the theory to describe the entire universe and its evolution.

However, this was only possible because physicists saw the universe as a smooth soup of particles. Only by ignoring those lumpy matter did they arrive at this model of the universe.

The cosmological principle made Einstein’s equations more applicable, but it also makes sense that the expansion of the universe should distribute matter more or less evenly.

Since then, astrophysicists have assumed this fairly simple model of the universe, but the problem is that they have found structures that violate the cosmological principle.

The 3D map shows the giant structures

Massive galaxy clusters only become visible when large parts of the universe are mapped in three dimensions. The most comprehensive survey is the Sloan Digital Sky Survey, which is the result of 20 years of data collection with a telescope in New Mexico, USA.

The catalog of millions of galaxies and quasars – the brightest galactic nuclei – is available to all astronomers on Earth, and here, in particular, they have found some of the largest structures in the visible universe.

Back in 2003, a survey revealed a 1.37-billion-light-year-long “wall” of galaxies called the Sloan Great Wall – a row of giant clusters about a billion light-years away.

If Sloan’s Great Wall was isolated, the cosmological principle may have survived, but later on, more and more structures larger than galaxies or quasars were found – like Smiling Bow, whose location was also determined using data from Sloan Digital. clear the sky.

So the giant structures suggest that the Cosmic Standard Model needs an overhaul, and that physicists already have ideas for improvement.

Some of them work on heterogeneous cosmology, researching how the evolution of the universe is affected when giant structures are taken into account. Perhaps larger structures are not a problem in such a model of the universe.

Others argue that gravity acts differently than Einstein describes over enormous distances, causing inequality in the universe.

The third perspective is dark energy, a hypothetical form of energy in empty space that causes the universe to expand faster and faster. Dark energy is an integral part of the cosmological standard model and is described as constant. But according to some scientists, it can vary in time or space – or this hypothetical energy is not at all necessary to describe the universe.

The new cosmology can offer different accounts of the expansion of the universe and thus our history of it. This could mean that the universe is not 13.8 billion years old, as the Standard Model tells us.

But cosmologists are not yet ready to write off the cosmological principle entirely. Before canceling the tried-and-true theory, they would like a more accurate map of the universe with more details of the giant structures that have been found, which also shows if there is more.

Fortunately, there is hope – comprehensive mapping of the universe will begin as early as December 2023, using the newly built large Vera C. Rubin Observatory in Chile. This telescope will give astronomers more detailed images of more than half of the sky, allowing them to see more into the past.

This designation will show whether it makes sense to see the universe as a smooth soup, or whether balls are floating in it. If the night sky isn’t the same – on a large scale – no matter what planet we’re on and in what direction we’re looking, it’s time for a new model of the universe.