Cosmologists at the University of California at Riverside used a cosmological tool and a new technique to calculate how much matter is in the universe.
To calculate it, the scientists first counted the matter in a single galaxy by observing how it orbits neighbouring galaxies, and then they scaled the amount for the entire universe.
The team found that matter makes up 31% of the universe, the rest is dark energy, an “unknown form of energy” that scientists still don’t understand.
According to the study authors, of that 31%, 80% is made up of dark matter, a substance that is only detected through its gravitational interactions with other matter. The amount of known matter – gas, dust, stars, galaxies, and planets – makes up only 20%.
Determining exactly how much matter is in the universe is not an easy task, cosmologists explained, noting that it depends on both observations and simulations.
“We have succeeded in making one of the most accurate measurements ever made using the galaxy cluster technique,” said co-author Gillian Wilson.
It is difficult to accurately measure the mass of any galaxy cluster because most of the matter is dark. Telescopes become useless. So a cosmological tool was used to measure the mass of a galaxy cluster using the orbits of its member galaxies.
“But it is difficult to measure the mass of any galaxy cluster accurately because most of the matter is dark and we cannot see it with telescopes,” he added.
Dark matter is a relatively unknown substance that is believed to be the gravitational glue that holds galaxies together. Calculations show that many galaxies would separate rather than rotate if they were not held together by a large amount of dark matter. It has never been directly observed and can only be seen through its gravitational interaction with other forms of matter.
To overcome this difficulty, astronomers developed GalWeight, a cosmological tool for measuring the mass of a galaxy cluster using the orbits of its member galaxies.
With the help of this tool, the researchers created a catalog of galaxy clusters. Finally, they compared the number of clusters in their new catalog with simulations to determine the total amount of matter in the universe.
“A great advantage of using our GalWeight galaxy orbit technique was that our team was able to determine a mass for each cluster individually rather than relying on more indirect statistical methods,” revealed co-author Anatoli Klipin.
The findings have been published in the Astrophysical Journal.