An international team of researchers has discovered the missing 50 percent of the visible matter in the universe. It turned out that matter is densely packed between galaxies and galactic clusters. The research preprint is published in the arXiv.org repository.
According to the Lambda-Cold Dark Matter (ΛCDM) cosmological model, the universe is more than 95 percent filled with dark matter and dark energy. Ordinary (baryonic) matter, made up of protons and neutrons, is only 4.6 percent. However, observations show that stars, the interstellar medium and hot gas of galactic clusters (clusters) contain only 50 percent of the theoretical amount of baryonic matter.
Matter in the Universe forms a three-dimensional network, the nodes of which are formed under the influence of the forces of gravity. These nodes, made up of galaxies or large galactic clusters and dark matter, are linked by threadlike structures. The results of hydrodynamic modeling showed that it is between galaxies and clusters that the missing part of ordinary matter should be located. It is called the warm-hot intergalactic environment (WHIM). However, it is difficult to detect due to its very low density.
The researchers analyzed data from the Planck orbiting observatory, designed to study the cosmic microwave background (relic radiation or CMB) left after the universe became transparent to thermal radiation. Scientists were looking for changes in the background caused by the passage of CMB photons through a warm-hot intergalactic medium, which could be located between the bright red galaxies (Luminous Red Galaxies). This phenomenon is called the Sunyaev - Zeldovich effect.
A total of 260 thousand galaxies have been studied. It turned out that in the threadlike structures between them, the baryonic matter is several times denser than the average in the Universe.