Matter found to comprise 31% of the total amount of matter and energy in the universe

"How much matter exists in the universe?" is one of cosmology's most intriguing and significant issues. Now, for the second time, the whole amount of matter has been successfully measured by an international team that includes experts from Chiba University. According to their findings, which were published in The Astrophysical Journal, matter makes up 31% of all matter and energy in the universe, with dark energy making up the remaining percentage.

First author Dr. Mohamed Abdullah, a researcher at the National Research Institute of Astronomy and Geophysics-Egypt, Chiba University, Japan, states that cosmologists believe that only about 20% of the total matter is made of regular or 'baryonic' matter, which includes stars, galaxies, atoms, and life. "Dark matter makes up about 80% of the universe; its nature is mysterious and may include some subatomic particles that have not yet been found."

"The team compared the observed number and mass of galaxy clusters per unit volume with predictions from numerical simulations, which is a well-proven technique to determine the total amount of matter in the universe," adds co-author Gillian Wilson, a physics professor and former graduate advisor of Abdullah who is also the vice chancellor for research, innovation, and economic development at UC Merced.

"Cluster abundance, or the number of clusters observed at present, is highly sensitive to cosmological conditions and, in particular, the total amount of matter."

According to University of Virginia researcher Anatoly Klypin, "more clusters would be formed if a larger percentage of the total matter in the universe was present." "However, since the majority of the matter in a galaxy cluster is dark and invisible to telescopes, it is challenging to determine its mass with accuracy."

The group was compelled to employ an indirect tracer of cluster mass in order to get around this obstacle. Their reliance was based on the mass richness relation (MRR), which states that galaxies are more abundant in more massive clusters than in less massive clusters. Since galaxies are made up of bright stars, one may infer the entire mass of a cluster by counting the number of galaxies inside it.

The scientists estimated the overall mass of each cluster by counting the number of galaxies in each sample taken from the Sloan Digital Sky Survey. The measured number and mass of galaxy clusters per unit volume were then compared to estimates from computer models.

A universe comprising 31% of all matter was the best fit between simulations and observations; this number was in great accord with that derived from cosmic microwave background (CMB) studies made by the Planck spacecraft. Interestingly, CMB is a whole another method.

According to Chiba University's Tomoaki Ishiyama, "We have succeeded in making the first measurement of matter density using the MRR, which is in excellent agreement with that obtained by the Planck team using the CMB method," "This study provides additional evidence that cluster abundance is a viable method for limiting cosmological parameters, and it can be used in conjunction with non-cluster approaches like gravitational lensing, Type Ia supernovae, baryon acoustic oscillations, and CMB anisotropies."

The group prides itself on being the first to accurately measure the distance to each cluster and the true member galaxies that are gravitationally bound to the cluster rather than background or foreground interlopers along the line of sight using spectroscopy, a technique that divides radiation into a spectrum of individual bands or colors.

In earlier attempts to use the MRR approach, the distances to each cluster and the neighboring galaxies that were genuine members were calculated using far less sophisticated and accurate imaging techniques, such as utilizing images of the sky taken at certain wavelengths.

In addition to demonstrating the effectiveness of the MRR technique for determining cosmological parameters, the paper published in The Astrophysical Journal also explains how it can be applied to new datasets obtained from spectroscopic galaxy surveys, including those conducted with the Subaru Telescope, the Dark Energy Survey, the Dark Energy Spectroscopic Instrument, the Euclid Telescope, the eROSITA Telescope, and the James Webb Space Telescope, as well as large-scale, wide-field imaging.