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EI2GYB > ASTRO 15.09.23 09:06l 171 Lines 7844 Bytes #999 (0) @ WW
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Subj: Matter comprises of 31% of the total amount of matter and e
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Matter comprises of 31% of the total amount of matter and energy in the universe
A research team relies on measuring the number of galaxy members to determine
the mass of galaxy clusters
Date:
September 13, 2023
Source:
Chiba University
Summary:
One of the most interesting and important questions in cosmology is, 'How
much matter exists in the universe?' An international team has now succeeded in
measuring the total amount of matter for the second time. The team determined
that matter makes up 31% of the total amount of matter and energy in the
universe, with the remainder consisting of dark energy.
One of the most interesting and important questions in cosmology is, "How much
matter exists in the universe?" An international team, including scientists at
Chiba University, has now succeeded in measuring the total amount of matter for
the second time. Reporting in The Astrophysical Journal, the team determined
that matter makes up 31% of the total amount of matter and energy in the
universe, with the remainder consisting of dark energy.
"Cosmologists believe that only about 20% of the total matter is made of
regular or 'baryonic' matter, which includes stars, galaxies, atoms, and life,"
explains first author Dr. Mohamed Abdullah, a researcher at the National
Research Institute of Astronomy and Geophysics-Egypt, Chiba University, Japan.
"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 used a well-proven technique to determine the total amount of matter
in the universe, which is to compare the observed number and mass of galaxy
clusters per unit volume with predictions from numerical simulations," says
co-author Gillian Wilson, Abdullah's former graduate advisor and Professor of
Physics and Vice Chancellor for research, innovation, and economic development
at UC Merced. "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."
"A higher percentage of the total matter in the universe would result in more
clusters being formed," says Anatoly Klypin from University of Virginia. "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 difficulty, the team was forced to use an indirect tracer of
cluster mass. They relied upon the fact that more massive clusters contain more
galaxies than less massive clusters (mass richness relation: MRR). Because
galaxies consist of luminous stars, the number of galaxies in each cluster can
be utilized as a way of indirectly determining its 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 of the clusters.
They were then able to compare the observed number and mass of galaxy clusters
per unit volume against predictions from numerical simulations. The best-fit
match between observations and simulations was with a universe consisting of
31% of the total matter, a value that was in excellent agreement with that
obtained using cosmic microwave background (CMB) observations from the Planck
satellite. Notably, CMB is a completely independent technique.
"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," says Tomoaki Ishiyama from Chiba University. "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."
The team credits their achievement as being the first to successfully utilize
spectroscopy, the technique that separates radiation into a spectrum of
individual bands or colors, to precisely determine 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.
Previous studies that attempted to use the MRR technique relied on much cruder
and less accurate imaging techniques, such as using pictures of the sky taken
at some wavelengths, to determine the distance to each cluster and the nearby
galaxies that were true members.
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