The Webb and Hubble telescopes confirm the rate of expansion of the universe, the puzzle remains

Webb's measurements shed new light on a decade-long mystery known as the Hubble voltage - the differences in the age of the universe between the Hubble observations and past observations that remain unexplained * Prof. Adam Ries, winner of the Nobel Prize in Physics for the discovery of dark energy, heads the project

The expansion rate of the universe, known as Hubble's constant, is one of the fundamental parameters for understanding the evolution and final fate of the universe. However, a consistent difference, called the "Hubble voltage", was found between the value of the constant as measured using a wide variety of independent distance ranges, and its value estimated from the post-Big Bang phosphorescence. NASA/ESA/CSA's James Webb Space Telescope has confirmed that the Hubble Space Telescope was right all along, erasing any remaining doubt about its measurements.

One of the scientific justifications for building the Hubble Space Telescope was to use its observational power to provide an accurate value for the expansion rate of the universe. Before Hubble's launch in 1990, observations from ground-based telescopes gave extremely wide ranges. Depending on the values ​​inferred for the expansion rate, the universe could be between 10 and 20 billion years old. Over the past 34 years, Hubble has narrowed this range to an accuracy of less than 13.8 percent, setting the age of the universe at XNUMX billion years. This was achieved by improving the so-called 'Cosmic Distance Scale' by measuring a class of stars known as variable Cepheids.

However, the value measured by the Hubble Space Telescope did not agree with other measurements suggesting that the universe expanded more rapidly after the Big Bang. These observations were made by ESA's Planck satellite by mapping the cosmic microwave background radiation - which is a marker of how the universe was supposed to develop after it cooled from the big bang.

The simple solution to the problem could have been to assume that perhaps Hubble's observations were wrong, as a result of an inaccuracy entering into the measurements of the bodies in deep space. Then the James Webb Space Telescope arrived, allowing astronomers to re-examine the Hubble results. Webb's infrared observations agreed with Hubble's visible light data.

In the end, the "stress tension" between what is happening in the near universe versus the expansion of the early universe remains a troubling puzzle for cosmologists. There may be a component to the fabric of space that we don't yet understand.

Does solving the gap require new physics, or is it the result of measurement errors between the two different methods of determining the rate of expansion of space?

Combined Webb and Hubble observations

Webb and Hubble have now collaborated to produce absolute measurements, reinforcing the case that something else – rather than measurement errors – is influencing the rate of expansion.

"When the measurement errors are removed from the equation, what's left is the very real and exciting possibility that we don't understand the universe," said Adam Reese, a physicist at Johns Hopkins University in Baltimore. Rees holds the Nobel Prize for the joint discovery that the expansion of the universe is accelerating, thanks to a phenomenon now called 'dark energy'.

As a secondary check, an initial observation by Webb in 2023 confirmed that Hubble's measurements of the expanding universe were correct. However, in trying to resolve the Hubble tension, some scientists wondered if invisible errors in measurement might increase and appear as we delve deeper into the universe. In particular, stellar density may affect brightness measurements of systematically more distant stars.

The SH0ES (Supernova H0 for the Equation of State of Dark Energy) team, led by Rees, made additional observations with a web of objects that are critical cosmic similarity points, known as variable cupids, which can now be compared with the Hubble data.

"We have now covered the entire range that Hubble observed, and we can rule out measurement error as the cause of Hubble's voltage with very high confidence," Rees said.

Webb's first observations in 2023 were successful in showing that Hubble was on the right track in reliably establishing the first rungs of the so-called 'Cosmic Distance Scale'.

Astronomers use different methods to measure relative distances in the universe, depending on the object being observed. including these techniques known as the 'Cosmic Distance Scale' - each step or measurement technique depends on the previous step to clarify.

Some researchers have suggested that, as we continue through the 'second phase', the cosmic distance scale may become less accurate if the measurements of Cepheids become less accurate with distance. Such inaccuracies can occur because a Cepheid's light can mix with that of a neighboring star, an effect that can become more pronounced with distance as the stars cluster closer together in the sky and become harder to distinguish.

The observational challenge is that previous Hubble images of more distant cupid stars appear more crowded and mixed with neighboring stars at greater distances between us and their host galaxies, requiring careful accounting for this effect. Dust in the way can further complicate the confidence in visible light measurements. Webb addresses this because it cuts through the dust and naturally isolates the Cepheids from neighboring stars because its vision is sharper than Hubble's at infrared wavelengths.

"A combination of Web and Hubble provides us with the best of both worlds. "We find that Hubble's measurements remain reliable as we move further up the cosmic distance scale," Rees said.

Webb's new observations included five host galaxies of eight type Ia supernovae containing a total of 1,000 cupids, and reached the most distant galaxy where reliable measurements of cupids have been made - NGC 5468, 130 million light-years away. "Thus we covered the entire range in which we performed measurements with the Hubble. However, we have reached the end of the second rung of the cosmic distance scale," said co-author Gagandeep Anand of the Space Telescope Science Institute in Baltimore, which operates the Webb and Hubble telescopes on behalf of NASA.

Together, Webb and Hubble's confirmation of the Hubble strain sets the stage for other observatories to potentially tackle the puzzle, including NASA's upcoming Nancy Grace Roman Space Telescope and ESA's recently launched Euclid mission.

Right now it's as if the distance scale observed by Hubble and Webb is a mooring point on one side of a river, and the post-Big Bang sunrise that Planck observed from the beginning of the universe is clearly anchored on the other side. The question of how the universe changed during the billions of years between these two points has not yet been directly observed. "We need to find out if we're missing something in how to connect the beginning of the universe to today," Rees said.

These findings were published in an issue ofFebruary 6, 2024 of The Astrophysical Journal Letters.

More of the topic in Hayadan:

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• Prof. Mario Livio: Adam Rees has a chance for a second Nobel * Proud of Dan Shechtman's achievement
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