An ultra-precise measurement of the composition of the Universe is shaking understanding of the cosmos

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Ultra-precise measurement of the composition of the Universe shakes understanding of the cosmos

Artistic illustration of the big bang.

The most precise measurement of the composition and expansion of the Universe confirms that “something is not quite right” in our understanding of the cosmos, according to the astrophysicists who carried out these calculations published on Wednesday.

The Universe we know is only about 5% visible matter, called baryonic. The rest is composed, the theory says, of dark matter and dark energy: two mysterious components that are believed to explain the physics of the cosmos as astronomers observe it.

The Astrophysical Journal.

Dark energy, believed to account for the remaining 66.2%, is believed to explain the phenomenon of the expanding Universe, which sees galaxies move further and further apart. faster.

To arrive at these numbers, an international team of scientists analyzed the light from 1,550 supernovae, stars that explode at the end of their lives, and the most distant ones ranging up to 10 billion light-years away, that is, dating back to a time when the Universe was only a quarter of its current age.

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We can compare them and see how the Universe behaves and evolves through time, Dillon Brout, of the Harvard-Smithsonian Center for Astrophysics and lead author of the 2008-2016 2016 2018 2016 Astrophysics Center, told AFP. study, dubbed Pantheon+.

This study tweaked the results of an earlier study. It represents the culmination of more than two decades of effort by observers and theorists around the world to decipher the essence of the cosmos, said astrophysicist Adam Reiss, Nobel Prize in Physics 2011, in a press release.

It was through the observation of supernovae in the late 1990s that Reiss and other researchers discovered that the expansion of the Universe was accelerating. It's like throwing a ball up in the air, and instead of falling, it keeps going up and accelerating, said Dillon Brout.

Pantheon+ joined its data to the SH0ES collaboration to arrive at the most accurate known measure of the speed of this expansion. That is, a rate of 73.4 kilometers per second per megaparsec (3.26 million light-years). In other words, a piece of the Universe more than 30 billion billion kilometers long stretches today at a speed of more than 260,000 km/h.

And that's the whole point. Because another way to measure the rate of expansion of the Universe relies on measuring the cosmic microwave background, the rest of the radiation that occurred soon after the big bang. And this calculation puts the expansion rate at 67 km/s/Mpc (megaparsec).

The difference between the two measurements is called Hubble's tension, du name of the American astronomer who brought a decisive understanding to the phenomenon of the remoteness of galaxies.

The precision of the results of Pantheon+ excludes that the Hubble tension is the fruit of chance. This indicates that potentially something is wrong with our understanding of the Universe, Dillon Brout told AFP. explain the discrepancy by the existence of another form of dark energy in the early ages of the Universe, with some kind of primordial magnetic fields, or by the fact that the Milky Way would find itself in a sort of cosmic vacuum slowing it down.

But at this point, concludes Brout, we scientists thrive on not understanding everything.< /p>

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