Like Goldilocks, the team compared the number of galaxy clusters measured with predictions from numerical simulations to determine which answer was “just right.” Image credit: Mohamed Abdullah (The National Research Institute of Astronomy and Geophysics, Egypt/Chiba University, Japan)

Scientists believe that the universe consists of three elements: normal matter, dark matter and dark energy. Ordinary matter consists of atoms that make up all the cosmic objects in the universe, but it makes up the smallest proportion of the universe. Due to the mysterious and dark nature of dark energy and dark matter, it is difficult to determine exactly how much of the universe they represent. But what about it? How much matter is there in the universe? An international team, including scientists from Chiba University, used a proven technique to calculate the amount of ordinary matter in the universe: they compared the observed quantity and mass of galaxy clusters per unit volume with predictions from numerical simulations. In a new study, scientists have succeeded in measuring the total amount of matter for a second time. They found that matter makes up 31% of the total amount of matter and energy in the universe, with the rest being dark energy.

in fact, larger clusters contain more galaxies than smaller clusters (mass richness relationship: MRR). The cluster mass richness relationship (MRR) is an effective and potentially powerful cosmological tool to constrain matter density and fluctuation amplitudes using cluster abundance techniques. Since galaxies are made up of bright stars, counting the number of galaxies in a cluster can be used to infer its overall mass. Scientists determined the total mass of each cluster by counting the number of galaxies in each cluster in their Sloan Digital Sky Survey sample. The number and mass of galaxy clusters found per unit volume were then compared with predictions from computer models. The amount of matter in the universe that gives the best agreement between observations and simulations is 31%, completely consistent with the results of the Planck satellite study of the cosmic microwave background (CMB). “We have succeeded in making the first measurement of matter density using MRR, which is in complete agreement with the results obtained by the Planck team using the CMB method,” said Tomoaki Ishiyama from Chiba University.

The number and mass of galaxy clusters found per unit volume were then compared with predictions from computer models. The amount of matter in the universe that gives the best agreement between observations and simulations is 31%, completely consistent with the results of the Planck satellite study of the cosmic microwave background (CMB). “We have succeeded in making the first measurement of matter density using MRR, which is in complete agreement with the results obtained by the Planck team using the CMB method,” said Tomoaki Ishiyama from Chiba University. This work further demonstrates that cluster abundance is a competitive technique for constraining cosmological parameters complementary to non-cluster techniques such as CMB anisotropy, baryonic acoustic oscillations, type supernovae Ia or gravitational lens. The study demonstrates that the MRR technique is a powerful tool for determining cosmological parameters. It also explains how it can be applied to newly available data sets from large-scale, deep-field imaging and spectroscopic studies of galaxies, such as those carried out with the Subaru Astronomy, Dark Energy Survey, Dark Energy Spectroscopic Instrument, Euclid Telescope, eROSITA. telescope and the James Webb Space Telescope.

Source: Astrophysical Journal. DOI: 10.3847/1538-4357/ace773