University of California, Riverside | 2020 Sep 18
A top goal in cosmology is to precisely measure the total amount of matter in the universe, a daunting exercise for even the most mathematically proficient. A team led by scientists at the University of California, Riverside, has now done just that. ... 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.
- The team determined that matter makes up about 31% of the total amount of matter and energy in the universe. Cosmologists believe about 20% of the total matter is made of regular — or “baryonic” matter — which includes stars, galaxies, atoms, and life, while about 80% is made of dark matter, whose mysterious nature is not yet known but may consist of some as-yet-undiscovered subatomic particle. (Credit: UCR/Mohamed Abdullah)
“To put that amount of matter in context, if all the matter in the universe were spread out evenly across space, it would correspond to an average mass density equal to only about six hydrogen atoms per cubic meter,” said first author Mohamed Abdullah ... “However, since we know 80% of matter is actually dark matter, in reality, most of this matter consists not of hydrogen atoms but rather of a type of matter which cosmologists don’t yet understand.”
Abdullah explained that one well-proven technique 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 predictions from numerical simulations. Because present-day galaxy clusters have formed from matter that has collapsed over billions of years under its own gravity, the number of clusters observed at the present time is very sensitive to cosmological conditions and, in particular, the total amount of matter. ...
Cosmological Constraints on Ωm and σ8 from Cluster Abundances Using the GalWCat19
Optical-Spectroscopic SDSS Catalog ~ Mohamed H. Abdullah, Anatoly Klypin, Gillian Wilson