New Analysis of Webb Data Measures Universe’s Expansion Rate, Reveals There May Be No ‘Hubble Tension’

We know a lot about our universe, but astronomers still debate exactly how fast it’s expanding. In fact, over the past two decades, two major methods of measuring this number, known as the Hubble constant, have given different answers, leading some to wonder if there’s something missing from our model of how the universe works.

But new measurements from the powerful James Webb Space Telescope seem to suggest that there may be no conflict, also known as the “Hubble tension,” after all.

In an article submitted to The Journal of Astrophysicscurrently available on the arXiv Wendy Freedman, a cosmologist at the University of Chicago, and her colleagues analyzed new data collected by NASA’s powerful James Webb Space Telescope. They measured the distances of 10 nearby galaxies and came up with a new value for how fast the universe is currently expanding.

Their measurement, 70 kilometers per second per megaparsec, overlaps with the other main method for the Hubble constant.

“Based on these new JWST data and three independent methods, we do not find strong evidence for a Hubble tension,” said Freedman, a renowned astronomer and professor of astronomy and astrophysics at the John and Marion Sullivan University in Chicago. “Instead, it appears that our standard cosmological model for explaining the evolution of the universe holds.”

Hubble telescope voltage?

We’ve known that the universe has been expanding since 1929, when UChicago alumnus Edwin Hubble (SB 1910, Ph.D. 1917) made measurements of stars that indicated that more distant galaxies were moving away from Earth faster than nearby galaxies. But it’s surprisingly difficult to determine precisely how fast the universe is expanding right now.

This number, known as the Hubble constant, is essential to understanding the history of the universe. It is a key part of our model of how the universe has evolved over time.

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

Given the importance and difficulty of making these measurements, scientists test them with different methods to ensure they are as accurate as possible.

One of the main approaches is to study the residual light from the Big Bang, known as the cosmic microwave background. The best current estimate of the Hubble constant using this method, which is very precise, is 67.4 kilometers per second per megaparsec.

The second major method, which Freedman specializes in, is to directly measure the expansion of galaxies in our local cosmic neighborhood, using stars whose brightness is known. Just as car headlights appear dimmer the farther away they are, at greater and greater distances, stars appear dimmer and dimmer. Measuring the distances and speed at which galaxies are moving away from us then tells us how fast the universe is expanding.

In the past, measurements made using this method have given a higher figure for the Hubble constant, closer to 74 kilometers per second per megaparsec.

This difference is significant enough that some scientists speculate that something important might be missing from our standard model of the evolution of the universe. For example, because one method looks at the early days of the universe and the other at the present, perhaps something important has changed in the universe over time. This apparent discrepancy is known as the “Hubble tension.”

Webb joins the dance

The James Webb Space Telescope, or JWST, offers humanity a powerful new tool for peering into the depths of space. Launched in 2021, the successor to the Hubble telescope has taken stunningly sharp images, revealed new aspects of distant worlds, and collected unprecedented data, opening new windows on the universe.

Freedman and his colleagues used the telescope to make measurements of ten nearby galaxies that provide a basis for measuring the expansion rate of the universe.

To test their results, they used three independent methods. The first uses a type of star known as a Cepheid variable star, whose brightness varies predictably over time. The second method is known as the “tip of the red giant branch,” and uses the fact that low-mass stars have a fixed upper limit on their brightness.

The third, most recent 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, within the same galaxies.

In each case, the values ​​were within the margin of error of the value given by the cosmic microwave background method of 67.4 kilometers per second per megaparsec.

“Getting a good match between three completely different types of stars is, for us, a strong indicator that we are on the right track,” Freedman said.

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