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Tuesday, 29 October 2019

The expansion of the universe is much faster than expected, causing a "crisis of cosmology"

Experimentally confirmed at the beginning of the 20th century, the expansion of the Universe is a dynamic phenomenon resulting in a recessionary movement of the galaxies . In 1998, cosmologists Adam Riess and Saul Perlmutter demonstrate that this expansion is accelerating. From there, many measurements of the rate of expansion will be made via the Hubble constant. However, to the surprise of cosmologists, a problem has emerged: the different measured values ​​do not agree with each other. The values ​​determined by the study of the cosmic microwave background (Planck) do not correspond to the values ​​determined via the study of quasars (H0liCOW, etc.). In other words, the acceleration of expansion is faster than the standard cosmological model predicts.

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A team of researchers confirmed this dilemma via data collected using a new telescope technology based on shape-changing mirrors. According to their study, published in the journal MNRAS , accurate measurements of the rate of expansion of the Universe do not correspond to the standard model used by cosmologists for decades. Other studies published earlier this year have reached similar conclusions.

" This is where the crisis of cosmology lies, " says Chris Fassnacht, astrophysicist. " This inadequacy is growing and has reached such a point that it is really no longer possible to consider it a coincidence. This disparity could not plausibly happen by chance, "said Adam Riess, a Nobel Prize winner for physics, for highlighting the acceleration of expansion.

Expansion 9% faster than predicted by standard cosmological model

To determine the rate of expansion of the Universe, in a way the speed at which expansion occurs, cosmologists study the cosmic microwave background (CMB). Based on these observations, they found that after the Big Bang, the Universe had first developed very rapidly. Then, expansion slowed down under the gravitational effect of dark matter. However, current measurements of the Hubble constant show that the expansion accelerates much faster than predicted by the standard model of cosmology.

Illustration showing the three basic steps that astronomers use to calculate the speed at which the universe expands over time, a value called Hubble's constant. All steps involve the construction of a "cosmic distance scale", starting by measuring precise distances to nearby galaxies and then moving to more distant galaxies. This "scale" consists of a series of measurements of different types of astronomical objects having a certain luminosity, which researchers can then use to calculate distances. Credits: NASA / ESA / A. Feild (STScI)

Riess's April study found that the Universe was growing 9% faster than predicted by CMB-based calculations. " It's not just two experiences that disagree. We measure something fundamentally different. One is a measure of the speed at which the Universe is developing today, as we see it. The other is a prediction based on the physics of the young Universe and on measures of the speed with which it should develop. If these values ​​do not match, it is very likely that we miss something ".

A difference in values ​​confirmed by the study of quasars

For the new study, researchers used a state-of-the-art mirror system at the Keck Observatory telescope in Hawaii. The camera uses flexible mirrors capable of correcting distortions caused by the Earth's atmosphere and rendering extremely clear images of objects in the sky. The researchers directed the telescope to three bright, highly active galaxy systems, called quasars.

They studied quasars using a process called the gravitational lens , which measures how light bends when moving around massive objects on its path to Earth. A massive object (like a giant galaxy, for example) bends the light in different directions, allowing scientists to see different distorted versions of the same quasar, at times slightly different from its past.

Images of the three quasars used in the study. Credits: G Chen / C Fassnacht / UC Davs

They can then compare these different images to calculate the time needed to light a quasar to reach us, and gather information about the development of the Universe during this period.

As in previous studies, the new results showed that the Universe was growing faster than expected by the standard model. The researchers compared their results to the Hubble Space Telescope data. The results obtained were consistent.

" A difference in the Hubble constant between early and late Universe means something is missing in our current standard model, " says astrophysicist Sherry Suyu. " For example, it could be a dark exotic energy, a new relativistic particle, or a new physics to discover ."


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