Observations with Webb confirm a challenge to cosmic theory

Dec. 9 () –

New observations with the James Webb Space Telescope offer a crucial check to address the discrepancy in measurements of the mysterious expansion of the universe.

The research, published in ‘The Astrophysical Journal’suggests that a new feature of the universe (not a flaw in telescope measurements) may be behind the decade-long mystery of why the universe is expanding faster today than in its infancy billions of years ago. The new data confirms Hubble Space Telescope measurements of the distances between nearby stars and galaxies.

Known as the Hubble strain, the discrepancy remains unexplained by even the best cosmological models.

The research is based on the discovery by Adam Riess, a Nobel Prize winner and professor of Physics and Astronomy at Johns Hopkins University, that the expansion of the universe is accelerating due to a mysterious “dark energy” that permeates vast expanses of space. between the stars and galaxies.

As the author explains in a statement: “The discrepancy between the observed expansion rate of the universe and the predictions of the Standard Model suggests that our understanding of the universe may be incomplete. Now that two flagship NASA telescopes mutually confirm their findings, we must take this issue very seriously. [de la tensión del Hubble]: “It’s a challenge, but also an incredible opportunity to learn more about our universe.”

Riess’ team used the largest sample of Webb data collected during its first two years in space to verify the Hubble telescope’s measurement of the universe’s expansion rate, a number known as the Hubble constant. They used three different methods to measure distances to supernova-hosting galaxies, focusing on distances previously measured by the Hubble telescope and known to produce the most precise “local” measurements of this number. Observations from both telescopes aligned closely, revealing Hubble measurements to be accurate and ruled out an inaccuracy large enough to attribute the tension to a Hubble error.

Still, the Hubble constant remains an enigma because measurements based on telescopic observations of the current universe produce higher values ​​compared to projections made using the “standard model of cosmology”a widely accepted framework for how the universe works calibrated with data from the cosmic microwave background, the weak radiation left over from the big bang.

While the Standard Model gives a Hubble constant of about 67-68 kilometers per second per megaparsec, measurements based on telescope observations regularly give a higher value of 70 to 76, with an average of 73 km/s/Mpc. This mismatch has baffled cosmologists for more than a decade because a difference of 5-6 km/s/Mpc is too large to be explained simply by flaws in measurement or observation technique. (Megaparsecs are enormous distances. Each is equivalent to 3.26 million light years, and a light year is the distance that light travels in one year: 9.4 trillion kilometers).

Since Webb’s new data rule out significant biases in Hubble’s measurements, the Hubble strain may be due to unknown factors or gaps in cosmologists’ understanding of physics yet to be discovered, Riess’ team reports.

“The Webb data is like looking at the universe in high definition for the first time and actually improve the signal-to-noise ratio of the measurements“says Siyang Li, a graduate student at Johns Hopkins University working on the study.

The new study covered about a third of Hubble’s entire sample of galaxies, using the known distance to a galaxy called NGC 4258 as a reference point. Even though the data set was smaller, the team achieved impressive precision, showing differences between measurements of less than 2%, much smaller than the approximate size of the 8-9% Hubble voltage discrepancy.

In addition to their analysis of pulsating stars called Cepheid variables, the gold standard for measuring cosmic distances, the team compared measurements based on carbon-rich stars and the brightest red giants in the same galaxies. All the galaxies observed by Webb together with their supernovae returned a Hubble constant of 72.6 km/s/Mpc, almost identical to the value of 72.8 km/s/Mpc found by Hubble for the same galaxies.

The study included Webb data samples from two groups working independently to refine the Hubble constant, one from Riess’ SH0ES team (Supernova, H 0 , for the dark energy equation of state) and another from Carnegie’s Hubble Program. -Chicago, as well as other teams. The combined measurements allow us to determine with greater precision so far the accuracy of the distances measured with the Cepheid stars of the Hubble telescope, which are fundamental to determining the Hubble constant.

Although the Hubble constant has no practical effect on the solar system, Earth, or everyday life, it reveals the evolution of the universe on extremely large scales, with vast areas of space stretching and push distant galaxies away from each other like raisins in sourdough. It is a key value that scientists use to map the structure of the universe, deepen their understanding of its state 13-14 billion years after the Big Bang, and calculate other fundamental aspects of the cosmos.

Resolving the Hubble tension could reveal new insights into more discrepancies with the standard cosmological model that have come to light in recent years, said Marc Kamionkowski, a Johns Hopkins cosmologist who helped calculate the Hubble constant and recently helped develop a possible new explanation for the tension.

The Standard Model explains the evolution of galaxies, the cosmic microwave background of the Big Bang, the abundance of chemical elements in the universe, and many other key observations based on the known laws of physics. However, it does not fully explain the nature of dark matter and dark energy, mysterious components of the universe. which are estimated to be responsible for 96% of its composition and its accelerated expansion.

“A possible explanation for the Hubble strain would be that something was missing from our understanding of the early universe, such as a new component of matter (early dark energy) that gave the universe an unexpected boost after the Big Bang,” says Kamionkowski, who did not participate in the new study. “And there are other ideas, such as the strange properties of dark matter, exotic particles, changing electronic masses or primordial magnetic fields that could work. “Theorists have license to be quite creative.”