The superclusters of galaxies, formed by the aggregation of galaxy clusters, are among the largest structures in the universe and come to contain thousands of galaxies and extend on scales of the order of hundreds of millions of light years. They are joined by filaments of galaxies in a complex geometry called the “Cosmic Web” that has been shown to be fractal up to lengths on the order of tens of millions of light-years. Studying the statistical properties of these formations is therefore crucial to understand the characteristics of the distribution of matter in the universe at large scales.
Along this line of research Giordano De Marzo, PhD student of CREF, Francesco Sylos Labini, research director of CREF and Luciano Pietronero, president of CREF, have recently concluded an analysis on the distribution of galaxy superclusters exploiting Zipf’s law and its generalized version of Zipf-Mandelbrot. The article, entitled “Zipf’s law for cosmic structures: how large are the greateststructures in the universe?” has been accepted by the prestigious journal Astronomy and Astrophysics and is already available on arXiv.
Comparing several catalogs and different definitions of the size of superclusters have found that superclusters follow Zipf’s law without deviations, unlike clusters that show instead strong deviations from that scaling law.
This result has significant implications about the properties of the distribution of matter in the universe. For example, it implies that this distribution is not self-mediating on the scales typical of superclusters and consequently different regions of the universe are characterized by significantly different statistical properties. Furthermore, the absence of deviations from Zipf’s law allows us to state that the largest supercluster contained in the analyzed catalogs is not a good estimator of the theoretical maximum, i.e., the largest possible supercluster. It follows that future observations will most likely identify larger structures than those observed to date.
Finally, the absence of a clear scale beyond which superclusters can no longer be found and the violation of the eigenmode property suggest that the data available to date are not sufficient to identify a possible crossover between fractal behavior and homogeneous matter distribution. This evidence opens new questions about the actual statistical properties of matter in the universe and the mechanisms of galaxy supercluster formation.