By Amit Malewar 16 Dec, 2024
Collected at: https://www.techexplorist.com/webb-telescopes-extensive-study-universe-expansion-challenges-cosmic-theory/94730/
The Hubble constant is still a mystery because measurements from telescopes in today’s universe give higher numbers than predictions made using the “standard model of cosmology,” a well-accepted idea of how the universe works. The standard model is based on data from the cosmic microwave background, the faint radiation left over from the Big Bang.
The standard model suggests the Hubble constant should be around 67-68 kilometers per second per megaparsec (a unit of distance in space). However, telescope measurements usually show values between 70 and 76, averaging 73 km/s/Mpc. This difference of 5-6 km/s/Mpc is too large to be explained by flaws in measurement or observation, leaving scientists puzzled for over ten years.
New observations from the James Webb Space Telescope suggest that a new feature in the universe, rather than errors in telescope measurements, might explain why the universe is expanding faster now than it did in its early stages billions of years ago.
The new data also supports the Hubble Space Telescope measurements, which looked at the distances between nearby stars and galaxies. This confirmation is an important step in solving the mystery of the universe’s unexpected expansion. The issue, known as the “Hubble tension,” remains unsolved, even by the most advanced cosmology models.
Nobel laureate and lead author Adam Riess, a Bloomberg Distinguished Professor of Physics and Astronomy at Johns Hopkins University, said, “The discrepancy between the observed expansion rate of the universe and the predictions of the standard model suggests that our understanding of the universe may be incomplete.”
“With two NASA flagship telescopes confirming each other’s findings, we must take this [Hubble tension] problem very seriously—it’s a challenge but also an incredible opportunity to learn more about our universe.”
This research is based on Riess’s Nobel Prize-winning discovery that the universe’s expansion is accelerating owing to a mysterious “dark energy” permeating vast stretches of space between stars and galaxies.
Riess’ team used the largest data the James Webb Space Telescope collected during its first two years in space to double-check the Hubble Space Telescope’s measurement of the universe’s expansion rate, known as the Hubble constant. They used three different methods to measure the distances to galaxies with supernovae, focusing on distances the Hubble telescope had already measured with high precision.
The results from both telescopes closely matched, confirming that the Hubble measurements are accurate and ruling out the idea that the Hubble tension is caused by any significant error in the Hubble telescope’s observations.
Since the new data from Webb confirms that there are no significant errors in Hubble’s measurements, according to Riess’ team, the Hubble tension might be caused by unknown factors or gaps in our understanding of physics that have yet to be discovered.
Siyang Li, a graduate student at Johns Hopkins University working on the study, explained, “The Webb data is like looking at the universe in high definition for the first time and improves the signal-to-noise of the measurements.”
The new study focused on about a third of Hubble’s full galaxy sample, using the known distance to the galaxy NGC 4258 as a reference. Even though the dataset was smaller, the team achieved impressive accuracy, with differences between measurements of less than 2%—much smaller than the roughly 8-9% discrepancy in the Hubble tension.
In addition to analyzing Cepheid variables, considered the gold standard for measuring cosmic distances, the team also cross-checked measurements using carbon-rich stars and the brightest red giants in the same galaxies.
All the galaxies observed by Webb and their supernovae gave a Hubble constant of 72.6 km/s/Mpc, almost identical to the 72.8 km/s/Mpc value found by Hubble for those same galaxies.
The study included Webb data from two independent groups working to refine the Hubble constant: Riess’ SH0ES team (Supernova, H0, for the Equation of State of Dark Energy) and the Carnegie-Chicago Hubble Program, as well as data from other teams.
The combined measurements provide the most precise determination yet of the accuracy of distances measured using the Hubble Telescope’s Cepheid stars, which are essential for determining the Hubble constant.
While the Hubble constant doesn’t directly impact our solar system, Earth, or daily life, it is crucial for understanding the evolution of the universe on vast scales. It helps explain how space itself is stretching, pushing distant galaxies away from each other, much like raisins moving apart in rising dough.
This value is essential for scientists to map the universe’s structure, explore its state 13-14 billion years after the Big Bang, and calculate other key aspects of the cosmos.
Solving the Hubble tension could lead to new insights into other discrepancies with the standard cosmological model, which have emerged in recent years, according to Marc Kamionkowski, a cosmologist at Johns Hopkins University. Kamionkowski, who helped calculate the Hubble constant, has also contributed to developing a potential new explanation for the tension.
The standard model of cosmology explains many key aspects of the universe, such as the evolution of galaxies, the cosmic microwave background from the Big Bang, the abundance of chemical elements, and other major observations, all based on known laws of physics. However, it doesn’t fully explain dark matter and energy, mysterious components that are thought to make up about 96% of the universe and responsible for its accelerated expansion.
Marc Kamionkowski, who was not involved in the new study, suggested that one possible explanation for the Hubble tension could be something missing in our understanding of the early universe, like a new component of matter known as “early dark energy.”
This could have given the universe an unexpected boost after the Big Bang. He also mentioned other ideas, such as strange properties of dark matter, exotic particles, changes in electron mass, or even primordial magnetic fields, which could potentially explain the tension. “Theorists have license to get pretty creative,” Kamionkowski added.
Journal Reference:
- Adam G. Riess, Dan Scolnic, Gagandeep S. Anand et al. JWST Validates HST Distance Measurements: Selection of Supernova Subsample Explains Differences in JWST Estimates of Local H0. The Astrophysical Journal. DOI 10.3847/1538-4357/ad8c21
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