It was found that matter constitutes 31% of the total amount of matter and energy in the universe

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

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

One of the most interesting and important questions in cosmology is “How much matter is there in the universe?” An international team, including scientists from Chiba University, has now succeeded in measuring the total amount of the substance for the second time. Report in Astrophysical JournalThe team found that matter constitutes 31% of the total amount of matter and energy in the universe, and the rest consists of dark energy.

“Cosmologists believe that only about 20% of total matter consists of ordinary or ‘baryonic’ matter, which includes stars, galaxies, atoms and life,” explains first author Dr. Mohamed Abdallah, a researcher at the National Research Institute for Astronomy and Geophysics-Egypt, Chiba University. Japan. “About 80% of it consists of dark matter, the mysterious nature of which is not yet known, but which may consist of some subatomic particles that have not yet been discovered.”

“The team used a proven technique to determine the total amount of matter in the universe, which was to compare the observed number and mass of galaxy clusters per unit volume with predictions from numerical simulations,” says co-author Gillian Wilson, from Abdullah University. Former graduate advisor and professor of physics and vice chancellor for research, innovation and economic development at the University of California, Merced.

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“The number of clusters observed at present, the so-called ‘cluster abundance’, is very sensitive to cosmic conditions and, in particular, to the total amount of matter.”

“A higher proportion of the total matter in the universe will lead to the formation of more clusters,” says Anatoly Klepin of the University of Virginia. “But it is difficult to accurately measure the mass of any galaxy cluster, as most of the matter is dark, and we cannot see it directly with telescopes.”

To overcome this difficulty, the team had to use an indirect cluster mass tracer. They relied on the fact that more massive clusters contain more galaxies than less massive clusters (mass richness relationship: MRR). Since galaxies are composed of luminous stars, the number of galaxies in each group can be used as a way to indirectly determine their total mass.

By measuring the number of galaxies in each cluster in their sample from the Sloan Digital Sky Survey, the team was able to estimate the total mass of each cluster. They were then able to compare the observed number and mass of galaxy clusters per unit volume with predictions from numerical simulations.

The best match between the observations and simulations was a universe consisting of 31% total matter, a value in excellent agreement with that obtained using cosmic microwave background (CMB) observations from the Planck satellite. It is worth noting that CMB is a completely independent technology.

“We have succeeded in making the first measurement of matter density using MRR, which is in excellent agreement with what the Planck team obtained using the CMB method,” says Tomoaki Ishiyama of Chiba University. “This work also shows that cluster abundance is a competitive technique for constraining cosmological parameters and complementary to non-cluster techniques such as CMB anisotropy, baryonic acoustic oscillations, Type Ia supernovae, or gravitational lensing.”

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The team credits its accomplishment with being the first to successfully use spectroscopy, a technique that separates radiation into a range of individual bands or colors, to precisely determine the distance to each cluster and the true member galaxies gravitationally bound to the cluster rather than the galaxies. Intrusive background or foreground along the line of sight.

Previous studies that attempted to use MRR relied on more primitive and less precise imaging techniques, such as using images of the sky taken at certain wavelengths, to determine the distance to each cluster and which nearby galaxies were actual members.

Paper published in Astrophysical Journalnot only shows that the MRR technique is a powerful tool for determining cosmological parameters, but also explains how it can be applied to new datasets available from large, wide and deep imaging, and spectroscopic surveys of galaxies such as those performed with the Subaru Telescope, the Dark Energy Survey, and the Spectroscopic Instrument. Dark Energy, Euclid Telescope, Aeroceta Telescope, and James Webb Space Telescope.

more information:
Muhammad Abdullah et al., Constraining cosmological parameters using the relationship between mass and richness, Astrophysical Journal (2023). doi: 10.3847/1538-4357/ace773

Magazine information:
Astrophysical Journal


Provided by Chiba University

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