Secret remains: James Webb measures the rate of expansion of the Universe

Astronomers used the James Webb Space Telescope (JWST) to measure the rate of expansion of the universe. Its data confirmed the results of observations by the Hubble telescope. This indicates the reality of the so-called “Hubble Tension”. 

Hubble Tension

Since the Big Bang, our universe has been continuously expanding. This process is described by Hubble’s Law, the key component of which is the Hubble constant, a coefficient that makes it possible to relate the distance to an object in the universe to its speed.

The history of the expansion of the universe. Source: NASA/WMAP Science Team

Astronomers have long been trying to calculate the exact value of the Hubble constant using various methods. During these attempts, they encountered an unexpected problem: the discrepancy between the values obtained. Thus, observations made using the Hubble telescope showed that the coefficient value is 74 km/s per megaparsec. At the same time, data from the Planck mission, which calculated the rate of expansion of the Universe by observing the relict cosmic microwave background, gives a completely different number: 68 km/s per megaparsec.

This discrepancy, called the “Hubble Tension,” is one of the main mysteries of modern cosmology. Of course, the simplest explanation is that one of the data sets contains errors, which explain the discrepancy. Therefore, astronomers have repeatedly verified the results of Hubble’s observations, making more and more new observations. But each time they only confirmed the received figure.

James Webb’s Control Check

After the launch of JWST, it was decided to use it for independent verification of Hubble. Astronomers have focused on Cepheids, variable stars whose distance measurements make up the second rung of the “ladder” of cosmic distances. They are usually used to determine the distance to galaxies.

Galaxy NGC 5468, which contains the Cepheids used to verify the accuracy of Hubble observations. Source: NASA, ESA, CSA, STScI, Adam G. Riess (JHU, STScI)

Some researchers have suggested that the light of Сepheids may mix with the light of neighboring stars, affecting the accuracy of measurements. JWST was used to verify this assumption. Its observations covered five galaxies that are home to more than a thousand Cepheids, as well as eight Type Ia supernovae. The latter emit the same amount of energy and are therefore used by astronomers as standard candles for calibrating and calculating distances for more distant galaxies, where it is no longer possible to see Cepheids.

The image of the Cepheid taken by the James Webb Telescope (left) and the Hubble Telescope (right). Source: NASA, ESA, CSA, STScI, Adam G. Riess (JHU, STScI)

JWST has confirmed the reliability of Hubble’s measurements. This means that the “Hubble Tension” is unlikely to be caused by measurement errors, and astronomers should focus on finding other explanations for its mystery.

According to

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