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Astrophysicists calculate the total amount of matter in the universe

The what’s this that makes up our universe is difficult to measure, to put it mildly. We know that most of the matter-energy density of the universe is made up of dark energy, the mysterious unknown force that drives the expansion of the universe. And we know the rest is matter, both normal and dark.

Figuring out the proportions of these three accurately is a challenge, but the researchers now say they have made one of the most accurate measurements to date to determine the proportion of matter.

According to their calculations, normal matter and dark matter combined make up 31.5% of the matter-energy density of the universe. The remaining 68.5% is dark energy.

“To put that amount of matter in context, if all matter in the universe were evenly distributed in space, it would correspond to an average mass density of just six hydrogen atoms per cubic meter”

;, said astronomer Mohamed Abdullah of the University of California, Riverside and the National Research Institute of Astronomy and Geophysics in Egypt.

“However, since we know that 80% of matter is actually dark matter, in reality most of this matter is not made up of hydrogen atoms, but rather of a type of matter that cosmologists do not yet understand.”

Understanding dark energy is actually crucial to our understanding of the Universe. We don’t know exactly what it is – the “darkness” in the name refers to that mystery – but it appears to be the force driving the expansion of the Universe, the speed of which has proved incredibly difficult to restrict in the past. a certain point.

Once we have a better understanding of the rate of expansion, it will improve our understanding of the evolution of the Universe as a whole. Hence, limiting the properties of dark energy is a rather important undertaking for cosmology in general, and there are many ways to do this.

Abdullah and his team used a method based on how things move in galaxy clusters – groups of up to thousands of gravitationally bound galaxies.

In general, galaxy clusters are a good tool for measuring matter in the universe. This is because they are made up of matter that gathered during the lifetime of the Universe, about 13.8 billion years, under gravity.

The number of clusters that we can observe in a volume of space is highly sensitive to the amount of matter, so counting them can provide a reasonable measure. But, again, it’s not an easy task.

“A higher percentage of matter would result in more clusters,” Abdullah said.

“The Goldilocks challenge for our team was to measure the number of clusters and then determine which answer was” right. “But it is difficult to accurately measure the mass of a cluster of galaxies because most of the matter is dark. , so we can not see it with telescopes. “

The team found a way around this problem with a technique called GalWeight. It uses the orbits of galaxies in and around a cluster to determine which galaxies actually belong to a given cluster and which don’t, with an accuracy of over 98%. This, they said, provides a more accurate census of that cluster, in turn leading to more accurate mass computation.

“A huge benefit of using our GalWeight galactic orbit technique was that our team was able to determine a mass for each cluster individually rather than relying on more indirect statistical methods,” explained astronomer Anatoly Klypin. of New Mexico State University.

The team applied their technique to observations collected by the Sloan Digital Sky Survey and created a catalog of galaxy clusters. These clusters were then compared with numerical simulations of galaxies to calculate the total amount of matter in the Universe.

The team’s result – 31.5% matter and 68.5% dark energy – is in close agreement with other measurements of the Universe’s matter-energy density.

“We were able to make one of the most accurate measurements ever made using the galaxy cluster technique,” said astronomer Gillian Wilson of UC Riverside.

“Furthermore, this is the first use of the galactic orbit technique that has obtained a value in agreement with those obtained by the teams that have used non-clustered techniques such as cosmic microwave background anisotropies, baryon acoustic oscillations, type supernovae. Ia or the gravitational lens “.

This result, the team says, demonstrates that GalWeight could prove to be a very useful tool for continuing to probe and limit the cosmological properties of the Universe.

The research was published in The Astrophysical Journal.

This article was originally published by ScienceAlert. Read the original article Here.

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