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“Maybe we misunderstood the universe.”

“Maybe we misunderstood the universe.”

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The Hubble effort remains one of the greatest mysteries in astrophysics. New research rules out measurement errors and raises new questions.

BALTIMORE – The question of how fast the universe is expanding seems simple, but it leads to one of the universe's greatest mysteries, the so-called Hubble tension. This mystery has puzzled astrophysicists for years, as two different ways of measuring the expansion of the universe lead to two different results.

Cosmic background radiation provides an expansion rate of about 67 kilometers per second per megaparsec (one megaparsec is equivalent to 3.26 million light-years). However, if you use Cepheids, a particular type of star, to measure distance, the result is an expansion rate of about 73 kilometers per second per megaparsec. This discrepancy between the two values ​​is the “Hubble tension,” for which no explanation has been found yet.

One cosmological question: How does Hubble tension happen?

Some scientists suspect that measurement error by the Hubble Space Telescope could be responsible for the “Hubble Potential.” However, this theory was refuted by a research team led by physicist Adam Reiss from Johns Hopkins University in Baltimore. “If measurement errors are excluded, there remains a real and exciting possibility that we have misunderstood the universe,” says Rees, who shared the Nobel Prize in Physics with other researchers in 2011 for discovering the accelerating expansion of the universe.

To check whether the Hubble Telescope produced measurement errors, the Reiss team used the James Webb Space Telescope (JWST). The results of their study were In the specialized magazine Astrophysical Journal Letters published.

Galaxy NGC 5468 is about 130 million light-years from Earth. It is the most distant galaxy in which the Hubble Space Telescope has discovered Cepheid stars, which are used to determine distances in astrophysics. The image was captured by a collaboration between the James Webb and Hubble space telescopes. © NASA, ESA, CSA, STScI, Adam G. Riess (JHU, STScI)

Does the Hubble Space Telescope have measurement error over long distances?

The “cosmic distance scale” is used to calculate the expansion of the universe. Each step of this ladder depends on the previous step, so measurement error passes through all steps. Cepheid stars, used to measure distances in space, can be difficult to measure at greater distances because their light can mix with the light of a nearby star and be difficult to separate. At least that was the fear when it came to data from the Hubble Space Telescope, because Hubble's images become less clear at greater distances.

Why are Cepheids used to measure distance?

Cepheid stars (stars with a variable pulsation) periodically change their brightness – this period is known very precisely. The luminosity and the period of brightness fluctuation are related to each other in Cepheids – which is why research can infer the distance to the star from the calculated brightness and luminosity.

On the other hand, the James Webb Space Telescope works perfectly, and thanks to its sharp infrared vision, it can see through all the dust in space and distinguish the stars better. “Combining Webb and Hubble gives us the best of both worlds. We have found that Hubble’s measurements remain reliable even as we move up the cosmic distance ladder,” explains Reiss. “We have now covered the entire region observed by Hubble and can “Ruling out measurement error as a cause of the Hubble effort with great certainty.”

The Hubble Telescope measures distances up to 130 million light-years

The new measurements reach a distance of 130 million light-years. “We have reached the end of the second step of the cosmic distance ladder,” asserts Gagandeep Anand of the Space Telescope Science Institute, which operates the Hubble and JWST space telescopes.

“We need to know if we missed something, and how we can connect the beginning of the universe to the present,” says Rees, summarizing the current situation. Two telescopes aiming to study the influence of dark energy in the universe could help: the European Space Agency's (ESA) Euclid space telescope is already active, and NASA's Nancy Grace Roman space telescope is scheduled to launch in 2027.

Only recently, the German space telescope eROSITA solved another cosmic mystery: the question of how matter is distributed and how much it is clumped. (unpaid bill)

The editor wrote this article and then used an AI language model to improve at her own discretion. All information has been carefully checked. Find out more about our AI principles here.