Scientists precisely measured the total amount of matter in the universe
One of the main goals of cosmological research is to precisely measure the total amount of matter contained in the cosmos. However, this can be a rather daunting task – even for the most mathematically adept scientists. But a team led by physicists from the University of California, Riverside has successfully taken on this challenge.
In a report published in the Astrophysical Journal, the team determined that matter collectively makes up only 31% of the total amount of matter and energy in the universe, while the rest is... dark energy.
This means that if all the matter in the universe were evenly distributed in space, it would correspond to an average mass density of only about six hydrogen atoms per cubic meter. "Since we know that 80% of this matter is actually dark matter, additionally most of this total matter (31%) does not consist of hydrogen atoms at all, but rather of some other, exotic matter that cosmologists do not yet understand," adds lead author Mohamed Abdullah, a doctoral student in the Department of Physics and Astronomy at UCR.
Abdullah notes that one of the well-established techniques for determining the total amount of matter in the universe is to compare the observed number and mass of galaxy clusters per unit volume with theoretical predictions derived from computer numerical simulations for the same cosmological parameters. Because modern galaxy clusters formed from matter that collapsed over billions of years under their own gravity, the number of currently observed clusters is very sensitive to these initial cosmological conditions, especially the total amount of matter in the cosmos.
"A higher proportion of matter present in the universe would result in a larger number of clusters," explains Abdullah. "The challenge for our team was to measure the number of clusters and then determine what result for it is the appropriate and optimal one. However, it is difficult to accurately measure the mass of any galaxy cluster because most of the matter they contain is dark matter, so we may not see it with our telescopes."
To overcome this observational difficulty, the team of astronomers from UCR first developed a new, highly accurate catalog called "GalWeight" – a publicly available catalog of galaxy clusters based on the large optical survey Sloan Digital Sky Survey (SDSS). Then the scientists compared the number of clusters in this new catalog with the number of clusters "produced" by cosmological computer simulations. This allowed them to determine the total amount of matter in the universe with considerable precision.
"We managed to make one of the most precise measurements ever performed using galaxy clusters," adds co-author Gillian Wilson, professor of physics and astronomy at UCR. "Moreover, this is the first use of the technique of so-called galactic orbits, which yielded a value consistent with values obtained by other teams using completely different techniques not related to clusters, such as anisotropy of the cosmic microwave background, baryon acoustic oscillations, Type Ia supernovae, and gravitational lensing."
"The great advantage of using the technique based on the GalWeight catalog is that our team was able to determine the mass for each cluster individually, rather than relying on more indirect statistical methods," summarizes third author Anatoly Klypin, an expert in numerical simulations and cosmology.
In the image above: The team determined that matter makes up about 31% of the total matter and energy in the universe. Cosmologists believe that about 20% of this total matter consists of regular – or "baryonic" matter – including stars, galaxies, atoms, and the building blocks of life, while about 80% consists of dark matter, whose mysterious nature is not yet known.
Source: UCR/Mohamed Abdullah
Combining their measurements with results from other teams using various other techniques, the UCR-led team was able to determine the most accurate total value of matter, stating that it accounts for 31.5 ± 1.3% of the total matter and energy in the universe.
The research was funded by grants from the National Science Foundation and NASA.
Read more:
- Original scientific paper: Cosmological Constraints on Ωm and σ8 from Cluster Abundances using the GalWCat19 Optical-spectroscopic SDSS Catalog, Mohamed H. Abdullah, AJ (2020)
- Full press article
Source: UCR
Editing: Elżbieta Kuligowska
In the image above: The team compared their measured number of galaxy clusters with predictions from numerical simulations.
Source: UCR/Mohamed Abdullah
