Based on data collected in one of the most extensive catalogs of cosmic objects in existence (called the SDSS), research carried out at the University of Central Lancashire has identified a huge structure that cannot be directly observed and is made up of millions of galaxies. one of the fundamental principles on which our knowledge of the universe is based, according to which the universe is homogeneous on a large scale in terms of the distribution of matter.
The Great Ring, the name used to describe this structure, is 1.3 billion light-years across and 9.2 billion light-years away from Earth. Despite being so far away, if it could be seen with the naked eye in the night sky, it would occupy an area equivalent to 15 full moons.
This is not the first time that astronomers have detected similar structures with such large dimensions. In addition, it happened that the new discovery was made by Alexia Lopez, a PhD student who had previously also found another even larger structure, called the Giant Arch.
A homogeneous universe in danger?
Our solar system is heterogeneous, with planets of various sizes and compositions. Likewise, the place the Sun occupies in the Milky Way is very different from the innermost region of the galaxy, where there is a greater density of stars. And the nearest galaxies, which together with ours form the so-called Local Group, are also very different from each other.
But as the perspective widens, these differences between regions gradually dilute, and the universe appears very homogeneous on a large scale. In such a way that when the universe is viewed from great distances, the distribution of huge clusters of galaxies (groups that can contain millions of galaxies) and the large empty spaces that exist between them appear similar.
Simulations made from catalogs of detected galaxies show us a very homogeneous and uniform universe on a large scale
All this led to what is known as the cosmological principle, which states that on a large scale there are no privileged regions or directions in the universe and that the distribution of matter is highly uniform. A consequence of the model is that the fragment of the universe that we observe from our position should also be homogeneous.
The detection of gigantic structures such as the Great Ring or the Giant Arc (and several others that are known) seems to challenge the Cosmological Principle, or at least may require it to remain valid, to contemplate the universe. on an even larger scale.
According to Alexia Lopez, “cosmologists have calculated that the maximum theoretical size of the structures is 1.2 billion light-years, and yet these two are much larger (the Giant Arc is 3 times larger, and the circumference of the Great Ring is comparable to the length of the Giant Arc). And he adds that the fact that the two structures are relatively close to each other is “extraordinarily fascinating.”
Perhaps part of an even larger structure
Although the Great Ring appears to have a circular shape in the sky, close examination shows that it would be more of a spiral, positioned in the way that its front shows us. The giant arc, 3.3 billion light years in size, has an almost symmetrical curved shape.
The great ring is the structure that can be seen surrounding the center in this diagram. Units on the axes represent millions of light years
The positions of these two large structures in the sky are relatively close, as they appear to be separated by only 12 visual degrees (this distance corresponds to 24 full moons in the sky). Moreover, they are located at about the same distance from Earth, about 9200 light years. This means that they existed when the universe was half its current age, and therefore due to the expansion of the universe, their separation must have been even smaller at that time. Therefore, for Alexia Lopez, the identification of two structures so extraordinarily large and so close together could indicate that they may be part of a larger configuration.
Possible origins
The formation of such immense structures could be due to the existence of hypothetical cosmic strings, entities that some cosmologists believe could have formed in the first moments of the big bang.
These hypothesized filaments of extremely thin dimensions (much smaller than atoms) but enormous lengths would have concentrated gigantic mass at the beginning of the universe and could have acted as the seeds around which the great structures of the universe were. created (one of the proponents of the existence of these cosmic strings is 2019 Nobel Prize in Physics Jim Peebles).
Lopez and his team suggest that another possibility to explain the origin of these structures would be to resort to new models of the evolution of the universe, such as the so-called conformal cyclic cosmology. A hypothesis advocated by, among others, Roger Penrose (2020 Nobel Prize in Physics), which shows that the universe is in an iterative evolution, with births occurring one after the other and in endless cycles.
Indirect detection
The discovery of these structures, which are not directly observable, was made through the analysis of the light of quasars, very distant (and therefore old) galaxies that we can observe thanks to the large amount of energy emitted by the matter falling towards us, the supermassive black hole that resides in it.
To reach our instruments, light from quasars had to travel great distances and pass through regions of space that contain concentrations of galaxies too faint to be observed.
Representation of a quasar, extremely distant galaxies with strong emission due to the action of their supermassive black holes
Therefore, during its journey, the radiation is affected by the interaction with the atoms of these concentrations of matter. The traces that the interactions have made in the light can be recognized by studying its spectrum (ie, the decomposition of light using a prism), which allows us to infer the presence of galaxies existing between us and distant quasars.
