Discovery of a row of galaxies so vast it challenges our understanding of the Universe

The Universe is filled with mysteries, and its large-scale observation by astronomers has only just begun. Recently, a researcher at the University of Central Lancashire made an astonishing discovery: a gigantic arc of galaxies (around 50) that spans 3.3 billion light years.

So that you can realize the magnitude of the discovery: the arc of galaxies in question makes about 3.5% of the observable universe! This structure, called the “Giant Arc”, calls into question one of the fundamental principles of cosmology.

Alexia Lopez, from the University of Central Lancashire (UK), spotted the arc by studying the light of around 40,000 quasars (distant galaxies with a very bright active nucleus). Indeed, this arc is not really visible in the night sky. If it was, it would be as long as 20 full moons side by side. She therefore looked for signs indicating that the light of the galaxies had been absorbed while passing through ionized magnesium, thus showing that it had passed through a cloud of gas surrounding the galaxy in question, located between the quasar and the Earth.

Lopez discovered that in the direction of the constellation Bouvier, between 45 and 50 galaxies or intermediate clusters of galaxies are arranged in an arc 3.3 billion light years long, at a distance from Earth of about 9.2 billion light years.

A questioning of the standard model of cosmology

If you had 15 giant arcs, they would extend from here to the limits of the observable universe Said Lopez, who presented this discovery on June 7 during the virtual meeting of theAmerican Astronomical Society. The observable universe is 93 billion light years wide, making it an important cosmological structure. According to Lopez, it is extremely unlikely (probability of only 0.0003%) that such a large structure could have been the result of chance.

3D animation showing the arc of galaxies (in red). © Alexia Lopez et al.

On the other hand, an important assumption of the Standard Model of the birth and evolution of the universe, the Cosmological Principle, indicates that it is very unlikely that such an arc exists, because over distances of more than 1.2 billion light years away, the universe should be roughly the same everywhere.

The arc adds to a handful of structures that don’t fit well with the cosmological principle. The new discovery intensifies the challenge they pose to the existing picture of the evolution of the universe. ” If the cosmological principle doesn’t hold up, our standard model of the universe collapses », Explains Lopez. ” There are alternative theories that may be able to help explain large-scale structures, but the Standard Model is based on the truth of the cosmological principle; we must have homogeneity and isotropy in the universe. It could have serious consequences “.


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