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“Maybe we misunderstood the universe.”

“Maybe we misunderstood the universe.”

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The question of how fast the universe is expanding is a headache in cosmology. Nobel Prize winner Adam Ries doesn't know what else to do.

BALTIMORE — Hubble tension is one of the universe's biggest mysteries — starting with a seemingly simple question: How fast is the universe expanding? But the answer is not at all simple and leads to a puzzle that astrophysics has been struggling with for many years. If you measure the expansion of the universe in two different ways, you will get two different results.

Using cosmic background radiation, we get an expansion rate of about 67 kilometers per second per megaparsec (one megaparsec is equivalent to 3.26 million light-years). If you use a type of star called Cepheids to measure distance, the expansion rate is about 73 kilometers per second per megaparsec. The discrepancy between the two values ​​is the “Hubble potential”, for which no explanation has been found yet.

It appears that the Hubble effort is not due to a measurement error

Some scientists had previously hoped that a measurement error by the Hubble Space Telescope might be behind the Hubble Effort. But a research team led by physicist Adam Ries of Johns Hopkins University in Baltimore is now dispelling that theory. Rees has been researching this field for a long time, and in 2011, he and other researchers were awarded the Nobel Prize in Physics for discovering that the expansion of the universe is accelerating.

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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)

“When you take into account measurement errors, what remains is the real and exciting possibility that we have got the universe wrong,” he says. The Nobel laureate and his team used the James Webb Space Telescope (JWST) to see if Hubble produced measurement errors. It was the study In the specialized magazine Astrophysical Journal Letters published.

The expansion of the universe is the greatest mystery in cosmology

To calculate the expansion of the universe, the so-called “cosmic distance ladder” is used. Each step of this ladder depends on the previous step – so measurement error occurs during all steps. Cepheid stars, which are used to determine distances in space, can also be difficult to measure at greater distances – for example, because their light mixes with the light of a nearby star and it is difficult to distinguish between the two.

Why are Cepheids used to measure distances?

Cepheid stars are called stars with variable pulsation. Its brightness changes periodically – this period is known very accurately. 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.

But while Hubble's images are becoming less clear at greater distances, the James Webb Space Telescope is working perfectly, and with its sharp infrared vision, it can see through all the dust in space and distinguish stars better. “Combining Webb and Hubble gives us the best of both worlds. “We found that Hubble’s measurements remain reliable even as we move up the cosmic distance scale,” says Rees. “We have now covered the entire range.” What Hubble observed and we can't rule out measurement error is definitely the cause of the Hubble effort.

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James Webb Space Telescope measurements extend 130 million light-years into the universe

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. notice together. Two telescopes aiming to study the influence of dark energy in the universe could help: the European Space Agency's 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)