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  • Siobhan Macrae (Editor & Contributing Writer)

Hubble Tension Webb & Hubble Unite to Confirm Universe Expansion

Updated: Mar 31

In recent observations, the James Webb Space Telescope has confirmed key measurements by the Hubble Space Telescope, further solidifying the cosmological puzzle known as the Hubble Tension. The discrepancy in the measurements suggests that there's a 1-in-a-million chance the mismatch is due to measurement errors.

Together, Hubble’s and Webb’s confirmation of the Hubble Tension sets up other observatories to possibly settle the mystery, including NASA’s upcoming Nancy Grace Roman Space Telescope and ESA’s recently launched Euclid mission.

The Data 

The latest Webb observations include five host galaxies housing eight Type Ia supernovae and a total of 1000 Cepheids. Among these observations is NGC 5468, located 130 million light-years away, where Cepheids have been extensively measured.

Webb's powerful infrared vision has also enabled the observation of Cepheid variable stars in galaxies like NGC 5584, which is visible at the top of one of the arms shown above. These findings align closely with observations from the Hubble Space Telescope, providing valuable insights into cosmic distances and the expansion of the universe. This combined dataset strengthens the case that the 'Hubble Tension' isn't solely due to measurement errors, further deepening the cosmic mystery. Astronomers have utilized Cepheid variable stars to measure distances across the Universe, providing essential data for calculating the Hubble constant, which determines the rate of the universe's expansion.

What's This Hubble tension all about?

This so called “Hubble Tension” refers to the discrepancy between the measurements of the universe’s expansion rate, known as the Hubble constant, obtained through different methods.

Observations from the Hubble Space Telescope, and now Webb, as well as other local measurements suggest a faster expansion rate for the universe, compared to predictions based on the Cosmic Microwave Background (CMB) and the standard model of cosmology.

  • Measurements using Cepheid variable stars suggest a rate of around 73 kilometers per second per megaparsec.

  • Analysis of the cosmic microwave background points to a slower rate, closer to 67 kilometers per second per megaparsec.

This tension has deepened with recent data from Webb, which confirmed the accuracy of Hubble’s measurements and added to the mystery. The Hubble constant is a crucial parameter for understanding the evolution and ultimate fate of the universe, and resolving this tension is a significant challenge in cosmology today.

Conflicting Measurements: This study presents a stark discrepancy between the expansion rate calculated from Cepheids and the rate predicted by the established cosmological model.

Cosmic Puzzle: This mismatch is extremely unlikely to be due to chance, suggesting a gap in our current understanding of how the universe works.

Rethinking the Model: Scientists may need to revise or find additions to the prevailing model of the universe to account for this discrepancy. Using Hubble and Webb data together, scientists say there is a 1-in-a-million chance that the mismatch is due to measurement errors.

In this image of galaxy NGC 5468, located 130 million light-years from Earth, which is one of the galaxies in which Hubble and Webb team up in as it is one of those Cepheid host galaxies. Hubble pinpointed Cepheid variable stars, vital for measuring the universe's expansion rate. This data was then cross-checked with a Type Ia supernova's intense light within the galaxy. Supernovae like this allow astronomers to probe even deeper into space, extending our understanding of how fast the universe is expanding.

The Webb team's response

"The simple solution to the dilemma would be to say that maybe the Hubble observations are wrong, as a result of some inaccuracy creeping into its measurements of the deep-space yardsticks. Then along came the James Webb Space Telescope, enabling astronomers to crosscheck Hubble’s results. Webb’s infrared views of Cepheids agreed with Hubble’s optical-light data. Webb confirmed that the Hubble telescope’s keen eye was right all along, erasing any lingering doubt about Hubble’s measurements."

"The bottom line is that the so-called Hubble Tension between what happens in the nearby Universe compared to the early Universe’s expansion remains a nagging puzzle for cosmologists. There may be something woven into the fabric of space that we don’t yet understand."

"Does resolving this discrepancy require new physics?"


In order to resolve the Hubble Tension, new physics may be needed, or existing models may have to be revised. As a result, cosmology remains an area of active research and exploration, demonstrating the significance of continuing to study and probe the universe.

This ongoing research and exploration in cosmology exemplify the essence of science itself - the constant evolution and adaptation of knowledge as new data and insights come to light. It is through the pursuit of understanding and probing the universe that our understanding of the cosmos continues to expand and change over time.


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