Washington (AFP)
A team of astrophysicists in the United States has obtained the most accurate measurement ever made of the total amount of matter in the universe, one of the most fascinating questions in cosmology.
The answer, published in The Astrophysical Journal on Monday, is that matter makes up 31.5% (plus or minus 1.3%) of the total amount of matter and energy that make up the universe.
The remaining 68.5% is dark energy, a mysterious force responsible for the expansion of the universe and whose existence was inferred from the observation of supernovas in the 1990s.
In other words, the total amount of matter in the observable universe is equivalent to 66,000,000,000,000,000,000,000,000 times the mass of the Sun, or 66,000 billion billions, the study's lead author Mohamed told AFP. Abdullah, PhD student in astrophysics at the University of California at Riverside.
80% of this matter is called dark matter, the nature of which remains mysterious, but one hypothesis of which is that it consists of subatomic particles.
The new measurement is close to the estimates made by other teams of astrophysicists using other cosmological techniques.
"It is the continuation of a long process which has allowed for 100 years to gradually become more and more precise", adds co-author Gillian Wilson, professor at the same university.
"It's nice to be able to measure such fundamental things about the universe without leaving planet Earth," she adds.
How do we weigh the universe?
The team used a 90-year-old technique that consists of observing the orbits of galaxies inside galaxy clusters (these clusters can contain hundreds or thousands of galaxies).
It is possible to calculate the gravitational force of each cluster, which allows their mass to be deduced.
- The fate of the universe -
Gillian Wilson explains that the technique was invented in the 1930s by Swiss astronomer Fritz Zwicky, a pioneer who was the first to hypothesize the existence of dark matter in galaxy clusters.
He had noticed that the gravitational mass of the galaxies in the Coma cluster was not enough to hold them together, and he had then suggested the presence of an invisible matter.
The University of California team improved Fritz Zwicky's technique and developed a tool called GalWeight to better classify which galaxy belongs to which cluster, then the researchers applied the tool to one of the three-dimensional maps the most. more detailed view of the universe, the Sloan Digital Sky Survey.
They measured the mass of 1,800 clusters of galaxies.
Then do computer simulations to find the optimal amount of matter in the universe corresponding to the real number of clusters, until you find the optimal value.
What can it be used for?
According to Gillian Wilson, the quest for the exact amount of matter in the universe will help us understand one of the greatest mysteries of the cosmos today, the nature of dark matter.
Further, "the total amount of dark matter and dark energy will tell us the fate of the universe," she said, with the current scientific consensus being that we are heading for a "Big Freeze", a "big freeze" also called "thermal death" of the universe, a state where the stars run out of fuel.
© 2020 AFP