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What’s the deal with the Universe? Scientists have the answer



A team of US astrophysicists has produced one of the most accurate measurements ever made of the total amount of matter in the Universe, a long-standing mystery of the cosmos.

The answer, published Monday in The Astrophysical Journal, is that matter is made up of 31.5% – from or takes 1.3% – of the total amount of matter and energy that makes up the Universe.

The remaining 68.5% is dark energy, a mysterious force that is accelerating the expansion of the Universe over time, and was first inferred from observations of distant supernovae in the late 1990s.

In other words, this means that the total amount of matter in the observable universe is equivalent to 66 billion trillion times the mass of our Sun, Mohamed Abdullah, an astrophysicist at the University of California, Riverside, and the AFP told AFP. ̵

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Most of this matter – 80% – is called dark matter. Its nature is not yet known, but it may consist of some undiscovered subatomic particle.

The latest measurements match well the values ​​previously found by other teams using different cosmological techniques, for example by measuring temperature fluctuations in the low-energy radiation left by the Big Bang.

“This has been a long process over the course of 100 years in which we are gradually becoming more and more accurate,” Gillian Wilson, study co-author and professor at UCR, told AFP.

“It’s just great to be able to make such a fundamental measurement of the Universe without leaving planet Earth,” he added.

So how exactly do you weigh the Universe?

The team honed a 90-year-old technique that involves observing how galaxies orbit within galaxy clusters – huge systems that contain thousands of galaxies.

These observations told them how strong the gravitational pull of each cluster of galaxies was, from which its total mass could then be calculated.

– Fate of the Universe –

In fact, Wilson explained, their technique was originally developed by the pioneer of astronomer Fritz Zwicky, who was the first person to suspect the existence of dark matter in galaxy clusters in the 1930s.

He noticed that the combined gravitational mass of the galaxies he had observed in the nearby Coma cluster of galaxies was insufficient to keep those galaxies from flying away from each other and realized that there must be another invisible matter at play.

The UCR team refined Zwicky’s technique by developing an instrument called GalWeight that more accurately determines which galaxies belong to a given cluster and which ones don’t.

They applied their instrument to the Sloan Digital Sky Survey, the most detailed three-dimensional maps of the Universe currently available, measuring the mass of 1,800 galaxy clusters and creating a catalog.

Finally, they compared the number of observed clusters per unit volume in their catalog with a series of computer simulations, each of which was given a different value for the total matter of the Universe.

Simulations with too much matter had too few clusters, while those with too much matter had too many clusters.

The “Goldilocks” value they found fits the simulations perfectly.

Wilson explained that having a more precise measure of the total amount of matter in the Universe can take us one step closer to learning the nature of dark matter, because “we know how much matter we should be looking for” when scientists perform particle experiments, for example. at the Large Hadron Collider.

Furthermore, “the total amount of dark matter and dark energy tells us the fate of the Universe,” he added, with the current scientific consensus being that we are headed for a “great freeze” in which galaxies move ever closer. leaves, and the stars in those galaxies eventually run out of fuel.

ia / ft


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