We know a lot about our universe, but astronomers are still debating how fast it’s expanding. In fact, over the past two decades, the two main ways to measure this number, known as the Hubble constant, have given different answers, leading some to wonder if there’s a problem with our model of how the universe works.

But new measurements by the powerful James Webb Space Telescope seem to suggest that the conflict, also known as the “Hubble tension,” may not actually be there.

In a submitted article Astrophysics Journal currently available on the preprint server arXiv University of Chicago cosmologist Wendy Friedman and colleagues analyzed new data from NASA’s powerful James Webb Space Telescope. They measured the distances to 10 nearby galaxies and came up with a new value for the universe’s current expansion rate.

Their measurement of 70 kilometers per second per megaparsec agrees with another important method for the Hubble constant.

“Based on these new JWST data and using three independent methods, we find no strong evidence for the Hubble tension,” said Friedman, a renowned astronomer and professor of astronomy and astrophysics at the John and Marion Sullivan University of the University of Chicago. “On the contrary, it appears that our standard cosmological model for explaining the evolution of the universe is valid.”

Hubble voltage?

We have known that the universe is expanding with time since 1929, when University of Chicago graduate Edwin Hubble (SB 1910, PhD 1917) showed from stellar measurements that the most distant galaxies were receding from Earth faster than nearby galaxies. But it is surprisingly difficult to put an exact figure on how fast the universe is currently expanding.

This number, known as the Hubble constant, is important for understanding the prehistory of the universe. It’s a key part of our model of how the universe evolved over time.

“Confirming the reality of the Hubble constant voltage would have important implications for both fundamental physics and modern cosmology,” Friedman explained.

Given the importance and complexity of making these measurements, scientists test them using a variety of methods to ensure they are as accurate as possible.

One important approach involves studying the light left over from the Big Bang, known as the cosmic microwave background. Using this method, the current best estimate of the Hubble constant is 67.4 kilometers per second per megaparsec, which is very accurate.

The second important method Friedman specializes in is directly measuring the expansion of galaxies in our local cosmic neighborhood, using stars of known brightness. Just as car lights appear dimmer as they move away, stars appear dimmer as they move farther away. Measuring the speed and distance at which galaxies are receding from us tells us how fast the universe is expanding.

In the past, measurements using this method have yielded higher Hubble constants of about 74 kilometers per second per megaparsec.

This difference is so large that some scientists suggest that our standard model of the universe’s evolution may be missing something important. For example, since one method looks at the earliest days of the universe and the other looks at the current era, it’s possible that something big has changed in the universe over time. This apparent discrepancy has become known as the “Hubble tension.”

The James Webb Space Telescope (JWST) offers humanity a powerful new tool for peering into deep space. The successor to the Hubble telescope, set to launch in 2021, has taken incredibly sharp images, revealed new aspects of distant worlds, and collected unprecedented data, opening new windows into the universe.

Friedman and his colleagues used the telescope to take measurements of ten nearby galaxies, which formed the basis for measuring the expansion rate of the universe.

They used three independent methods to cross-validate their results. The first uses a type of star known as a Cepheid variable, whose brightness varies predictably over time. The second method, known as the “red giant branch tip,” exploits the fact that low-mass stars reach a fixed upper limit on their brightness.

The third and newest method uses a type of star called carbon stars, which have consistent colors and brightnesses in the near-infrared light spectrum. The new analysis is the first to use all three methods simultaneously on the same galaxies.

In all cases, the values ​​were within the margin of error for the cosmic microwave background value of 67.4 kilometers per second per megaparsec.

“Getting a good deal on three completely different types of stars is a strong indication that we are on the right track,” Friedman said.

“Future observations with JWST will be critical to confirm or refute the Hubble tension and evaluate the implications for cosmology,” said Barry Madore, a co-author of the study from the Carnegie Institution for Science and a professor at the University of Chicago.