https://phys.org/news/2018-07-densest-clusters-galaxies-universe-revealed.html

Studying the cosmic web is one of the current challenges in astrophysics. The properties of the main components of matter on these scales are not well known, so we use terms such as "dark matter" and "dark energy" The former makes up around 20 percent of the mass of the universe and is what keeps the structures bound by their own gravity—it acts a bit like glue. The second, on the other hand, makes up 75 percent of the universe and is related to the way in which the universe expands. The "normal" matter, the galaxies with their stars, gas, and dust, make up barely 5 percent of the mass of the universe, but they play the important role in tracing the forces and the properties of the dark matter and dark energies.

An international team led by Mauro Sereno of the University of Bologna (Italy), with participation by the IAC and by the Instituto de Astrofísica de Andalucía (IAA), has located one of the densest clusters of galaxies in the universe. The study analyses, for the first time, the outer zones of the galaxy cluster PSZ2 G099.86+58.45 out to a radius of 90 million light years, a region in which the distribution of matter was not known previously, nor whether the material in these zones is bound together by the gravity of the cluster.