31% of the Universe: Matter’s Cosmic Share

A Breakthrough in Cosmic Matter Measurement: Matter Constitutes 31% of the Universe

One of the most profound inquiries in cosmology has always been, “How much matter truly exists in the vast expanse of our universe?” Now, an international team, including researchers from Chiba University, has accomplished the daunting task of measuring the total amount of matter for the second time. Their findings, published in The Astrophysical Journal, reveal that matter comprises a significant 31% of the entire cosmic matter and energy composition, leaving the remainder shrouded in the enigmatic veil of dark energy.

Dr. Abdullah, a scientist from the Research Institute of Astronomy and Geophysics-Egypt, Chiba University, Japan, explains, “About 80% is made of dark matter, whose mysterious nature is not yet known but may consist of some as-yet-undiscovered subatomic particles.”

The team employed a well-established methodology to ascertain the universe’s total matter content, involving the comparison of the observed number and mass of galaxy clusters per unit volume with predictions derived from numerical simulations. As co-author Gillian Wilson, Professor of Physics and Vice Chancellor for Research, Innovation, and Economic Development at UC Merced, elucidates, “The number of clusters observed at the present time, the so-called ‘cluster abundance,’ is very sensitive to cosmological conditions and, in particular, the total amount of matter.”

Anatoly Klypin from the University of Virginia adds, “A higher percentage of the total matter in the universe would result in more clusters being formed. But it is difficult to measure the mass of any galaxy cluster accurately as most of the matter is dark, and we cannot see it directly with telescopes.”

To overcome this challenge, the team resorted to an indirect indicator of cluster mass. They relied on the fact that more massive clusters house a greater number of galaxies compared to their less massive counterparts, known as the mass richness relation (MRR). Given that galaxies comprise luminous stars, the number of galaxies within each cluster offered an indirect means of estimating its total mass.

By quantifying the number of galaxies within each cluster through data from the Sloan Digital Sky Survey, the team calculated the total mass of each cluster. This information was then juxtaposed with predictions from numerical simulations, leading to a revelation—the universe’s composition consists of 31% matter. Remarkably, this figure closely aligns with that obtained through cosmic microwave background (CMB) observations conducted by the Planck satellite, a wholly independent method.

Tomoaki Ishiyama from Chiba University remarks, “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 work further demonstrates that cluster abundance is a competitive technique for constraining cosmological parameters and complementary to non-cluster techniques such as CMB anisotropies, baryon acoustic oscillations, Type Ia supernovae, or gravitational lensing.”

A pivotal aspect of their accomplishment was the integration of spectroscopy—a technique that dissects radiation into a spectrum of distinct bands or colors. Spectroscopy enabled precise determination of the distance to each cluster and the identification of true member galaxies gravitationally linked to the cluster, distinguishing them from background or foreground interlopers.

This breakthrough not only reinforces the effectiveness of the MRR technique in discerning cosmological parameters but also elucidates its potential applicability to forthcoming datasets from extensive imaging and spectroscopic galaxy surveys, including those conducted with instruments like the Subaru Telescope, Dark Energy Survey, Dark Energy Spectroscopic Instrument, Euclid Telescope, eROSITA Telescope, and the James Webb Space Telescope.

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Disclaimer: The views, suggestions, and opinions expressed here are the sole responsibility of the experts. No Citizen Wave journalist was involved in the writing and production of this article.

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