Thanks to modern transport and global communications, our planet no longer seems large to us, and in recent decades, the size of the solar system has ceased to confuse humanity, accustomed to flying automatic interplanetary stations. The space covered by our Galaxy is perceived by consciousness already much more difficult. If we had the opportunity to see it in its entirety, from the side, then we would not have distinguished a tiny, microscopic Sun.
Well, how do you realize the size of an object within which a single galaxy will seem like the smallest speck of dust? A striking example of such a gigantic formation of a cosmological scale is the so-called Great Wall of Sloan - one of the largest complexes known today to date, formed by galactic superclusters.
The structural hierarchy of the universe
It is most expedient to begin the consideration of the structural levels of the Universe with galaxies - rather large, massive systems. It is from the scale of galaxies that such an important cosmological factor as the dark (non-baryonic) substance begins to manifest itself.
Galaxies, as a rule, are united into groups and clusters - stable, gravitationally connected systems with sizes of the order of 10 7 light years. Clusters can contain up to hundreds of elements, but are usually structured by one or more giant galaxies.
The next level is superclusters, whose diameters are an order of magnitude larger. It was previously believed that they are completely gravitationally unrelated, and their components are subject only to the cosmological expansion of the Universe. However, flows were discovered inside the superclusters that are directed toward regions of increased mass concentration — attractors.
And finally, the highest level - galactic filaments: fibers, threads, walls. These are associations of superclusters, and, despite the participation of the latter in the Hubble stream, local centers of mass and internal motion clearly also exist within the threads and walls. These associations include the Great Wall of Sloan. In the photo above is her eastern section.
But visible, baryonic matter cannot serve as the basis for a large-scale structure - it is too small. The distribution of galaxies over clusters, superclusters, threads and walls merely reflects the “frame” created by flows and concentration nodes of dark, invisible matter.
Opening
In 2003, Princeton astronomers J. R. Gott and M. Juric and colleagues, who studied data from the Sloan Digital Sky Survey (SDSS), announced the discovery of an extremely large-scale galactic complex - a wall, which contains several giant superclusters. The structure received a name in honor of the founder of the fund from which the project was financed. Sometimes it is also called the Great Wall of the SDSS.
The newly discovered object immediately became the record holder in terms of length. Rough estimates give the value of several tens of thousands of galaxies of the Great Wall of Sloan. The photo below allows you to compare it (box 2) with other large formations within one and a half billion light years: superclusters of Shapley (1), Hours - Grids (3) and Pisces - Whale (4).
And now, after the discovery of larger structures, it remains one of the greatest phenomena of the universe.
Main characteristics
The wall is an elongated formation of complex configuration with a cross section close in shape to an ellipse strongly flattened along the minor axis. It stretched for 1.38 billion light-years through the regions of the constellations of Raven, Hydra and Centaurus. It is separated from us by an average distance of just over a billion light-years.
The map below shows the length of the Great Wall of Sloan compared to another similar structure located closer to us - the Great North, or the CfA wall, which was the first open galactic fiber. They vary in length by almost 3 times.
It may seem that such a gigantic complex, stretching over a significant part of the sky, is quite simple to study. Of course, this is not so. Any area of the sky is filled with radiation sources that are remote at various distances, and most of them need to be excluded. The sample of galaxies for the wall of interest to us is objects with redshifts in the range from 0.04 to 0.12.
Structural features
The structure of the Wall is investigated by the spatial distribution of its elements, the types of galaxies inhabiting clusters and superclusters in its composition, by the spectra of these galaxies, reflecting their age, features of motion and other characteristics.
Currently, two superclusters of galaxies of the Great Wall of Sloan are best studied: SCl 111 and SCl 136 (the largest). It is known that they differ significantly from each other in structure, shape, density, as well as in the types and dynamics of galaxies. This clearly indicates the different origin and development paths of superclusters. Smaller superclusters also have noticeable dissimilarities.
Perhaps such a clear differentiation of the components of the giant wall reflects the coincidence of their joint presence, and the Great Wall of SDSS is not at all a single, connected entity.
Conflict with Theory
With the enormous size of the Great Wall of the Sloan and even larger objects, discovered not so long ago, an important problem is connected. The fact is that the existence of such extended structures contradicts the cosmological principle. According to this principle, the Universe on a scale of over 250-300 million light-years should exhibit a homogeneous and isotropic distribution of matter. A good proof of this is the high degree of isotropy of the CMB radiation.
It is not yet clear how this task will be solved. It is possible that it is solvable in the framework of the modern cosmological model, which successfully explains most of the observed properties of our Universe in their relationship. Cosmology is an actively developing science, the success of which is associated, on the one hand, with the latest methods of observation and data processing, and, on the other, with the leading edge of theoretical physics. Further studies will undoubtedly clarify the question posed before her by the Great Wall of Sloan and similar phenomena, but, of course, put forward new, no less intriguing ones.