And it is that everything we see around us and with what we interact in our daily lives hardly represents a small fraction of what is in the cosmos. For a long time it was believed that the balance was roughly 32/68% between matter and energy, and even within that minority of matter, most of it is “dark.” Ordinary (or baryonic) matter only makes up about 5% of all that.
Critical density of the universe
Now, using a new and much more precise method, a team of researchers from the University of California at Riverside (USA) has managed to “weigh” the universe; that is, to measure with the maximum possible precision the amount of matter and energy it contains. By calculating the mass of hundreds of galaxy clusters, experts have found that matter makes up less than a third of the content of the universe.
Calculating how much matter is in the universe is not an easy task , so it takes a bit of creativity. The number of galaxy clusters in the local universe depends on the total amount of matter. If there were more matter, there would be more groups, so the challenge was to measure how massive those groups are and come up with the final figure.
“The challenge was to measure the number of clusters and then determine which answer was ‘correct.’ But it is difficult to measure the mass of any galaxy cluster with precision because most of the matter is dark, and cannot be seen with telescopes, “explains Mohamed Abdullah, leader of the study published in The Astrophysical Journal.
Weighing the universe
To make one of the most accurate measurements ever made of the universe, the researchers developed a cosmological tool called GalWeight, which uses the motion of galaxies in clusters to find a total mass. These values were then entered into a cosmological simulation and the final estimate was extracted from this.
“This is the first use of the galactic orbit technique that has obtained a value in accordance with those obtained by teams that used non-grouped techniques such as cosmic microwave background anisotropies, baryonic acoustic oscillations, type Ia supernovae or gravitational lenses”, says Gillian Wilson, co-author of the work.
In total, the new calculation shows that matter constitutes approximately 31.5% of the total content of the universe. 68.5% is dark energy, a mysterious force that seems to be driving the acceleration of the expansion of the universe.
“To put that amount of matter in context, if all the matter in the universe were evenly distributed in space, it would correspond to an average mass density equal to only about six hydrogen atoms per cubic meter,” says Abdullah. “However, since we know that 80% of matter is actually dark matter, in reality, most of this matter does not consist of hydrogen atoms, but rather a type of matter that cosmologists do not yet understand .”
What is dark energy?
Knowing exactly what dark energy is is crucial to our understanding of the universe . We do not know what it is, at the moment, hence its own name refers to the darkness of knowledge that it represents for us, but it seems to be the force that drives the expansion of the cosmos, whose speed has proven to be incredibly difficult to reduce past. a certain point.
Referencia: Mohamed H. Abdullah et al, Cosmological Constraints on Ω m and σ 8 from Cluster Abundances Using the GalWCat19 Optical-spectroscopic SDSS Catalog, The Astrophysical Journal (2020). DOI: 10.3847/1538-4357/aba619
