Calculating the amount of matter in the universe is a daunting task for even the most experienced cosmologists and astrophysicists, but it is also important for determining the accuracy of all measurements that depend on it. But a team at the University of California claims to have obtained accurate calculations.
According to the study, matter is responsible for 31% of the total amount of matter and energy in the universe. The other 69% consists of dark energy, a form of energy that is distributed throughout space, possibly responsible for the acceleration of the expansion rate of the universe.
As explained by the main author of the study Mohamed Abdullah, we can imagine a scenario in which all the existing matter is spread throughout the universe in a homogeneous way. If so, we would have a mass of density equivalent to about six hydrogen atoms per cubic meter. However, things are much more complex than that, especially if we consider dark matter, a type of matter that scientists still do not understand. In fact, 80% of the matter is dark matter.
To reach this result, Abdullah and his team used an already proven technique, which is to compare the number and mass of observed galaxy clusters with predictions from numerical simulations. “A higher percentage of material would result in more clusters,” said Abdullah. He explains that the team’s challenge was the difficulty “of accurately measuring the mass of any galaxy cluster because most of the matter is dark, so we cannot see it with telescopes.”
So how did they manage to estimate the amount of matter if you can’t see most of it? Well, the team developed a tool called “GalWeight”, capable of measuring the mass of a cluster of galaxies using the orbits of each galaxy individually. Using it in the notes of the Sloan Digital Sky Survey (a survey of astronomical data), the result was the “GalWCat19”, a catalog of galaxy clusters that is already available to the public.
Then, it was enough to compare the number of clusters in this catalog with the numerical simulations to determine the total amount of matter in the universe. According to co-author Gillian Wilson, this is “one of the most accurate measurements ever made using the galaxy cluster technique”. It is not the first time that this result has been obtained, but it is still of great importance because it is in accordance with the numbers found in other techniques that also set out to measure the matter of the universe.
Not only that, but the new study has an advantage over previous ones. Because instead of a calculation based on indirect statistics, this was the first time that scientists were able to measure the matter of the cosmos by measuring the mass of individual clusters – that is, a more direct method of observation. The study was published in the Astrophysical Journal.
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