Webb telescope may reveal how fast the universe is expanding

For over a century, humans have measured the universe with ever-improving tools, driven by a desire to understand where we come from and where we’re going. One of the most important numbers in cosmology is the Hubble constant, which tells us how fast the universe is expanding.

Yet, for the past decade, scientists have been deeply puzzled. Two different methods to measure this expansion gave conflicting results. If the universe could not agree with itself, perhaps our best theory of the cosmos was wrong.

Now, thanks to the power of the James Webb Space Telescope (JWST), the mystery of universe expansion may be unraveling. A new study led by Professor Wendy Freedman of the University of Chicago suggests the universe might not be at odds with itself after all.

Freedman, a central figure in this debate, has worked for years to test the cosmic numbers from every angle. “This new evidence is suggesting that our Standard Model of the universe is holding up,” she said.

Using Webb to test universe expansion

Astronomers use two main strategies to measure how fast the universe expands. The first approach looks deep into the past.

By studying the cosmic microwave background (CMB) – radiation from just after the Big Bang – scientists can estimate the early expansion rate. This method relies on data from satellites like Planck, which gives a value of about 67.4 kilometers per second per megaparsec.

The second method focuses on the nearby universe. This is where Freedman has made her mark. Her team measures how galaxies move away from us today.

That requires knowing how far those galaxies are. The challenge is that measuring such distances is extremely hard. It involves tracking stellar explosions called Type Ia supernovae, which serve as cosmic mileposts.

Freedman’s team spent years refining methods using supernovae and stars like red giants and Cepheids. These, aided by the Webb telescope, help anchor the cosmic distance ladder to measure universe expansion.

Viewing distant galaxies in new light

In their latest work, Freedman’s team used three distinct indicators: the Tip of the Red Giant Branch (TRGB), Cepheid variables, and JAGB stars (short for carbon-rich Asymptotic Giant Branch stars).

These stars shine at predictable brightnesses. By comparing their known brightness to how bright they appear from Earth, astronomers can calculate distances.

The JWST has made these measurements far more precise. Its infrared cameras can see through cosmic dust that previously clouded observations. It also resolves individual stars in distant galaxies that once appeared as fuzzy clusters.

These improvements significantly reduce the main sources of error that have plagued past studies.

Freedman’s team used JWST to measure ten galaxies with supernovae and anchored results to NGC 4258, improving consistency across methods.

Webb’s data reveals growth

Using JWST’s data, the team calculated a Hubble constant of 70.39 kilometers per second per megaparsec. The uncertainty is just ±1.22 (statistical). This number is notably consistent with the CMB value of 67.4, resolving the long-standing tension between early and late universe measurements.

“We’ve more than doubled our sample of galaxies used to calibrate the supernovae,” Freedman said. “The statistical improvement is significant. This considerably strengthens the result.”

The study also included rigorous checks. The team used a “blinding” technique, which means they analyzed the data without knowing the final result. Only after the analysis was complete did they look at the numbers. This method reduces bias and improves reliability.

Measuring the rate of expansion

One remarkable result was how closely the TRGB and JAGB methods agreed. In eight galaxies where both methods were used, the difference was less than one percent. That level of consistency boosts confidence in the accuracy of the measurements.

Combining all JWST and Hubble Space Telescope (HST) TRGB data across 24 galaxies, the team again got a Hubble constant of 70.39. The full uncertainties included ±1.22 (statistical), ±1.33 (systematic), and ±0.70 (from supernova scatter).

These overlapping results suggest that the methods are sound and the cosmic tension may have been due to earlier observational limits.

“We’re really seeing how fantastic the James Webb Space Telescope is for accurately measuring distances to galaxies,” said co-author Taylor Hoyt of the Lawrence Berkeley Laboratory.

“Using its infrared detectors, we can see through dust that has historically plagued accurate measurement of distances, and we can measure with much greater accuracy the brightnesses of stars,” added Barry Madore, of the Carnegie Institution for Science.

Exploring other cosmic mysteries

While the results strengthen the Standard Model of cosmology, Freedman isn’t declaring the mystery entirely solved. The paper emphasizes that there are still uncertainties, especially in the calibration of supernovae and the physics of distant stars.

However, the improved agreement between early and late measurements suggests that the Hubble constant may no longer be the place to search for cracks in the model.

Freedman notes that this doesn’t close the book on cosmic mysteries. Scientists still hope to understand dark energy and dark matter – two unseen forces that shape the universe. But at least for now, the tools we use to measure the universe appear more reliable than ever.

“There have been well over 1,000 papers trying to attack this problem, and it’s just turned out to be extraordinarily difficult to do,” she said.

Future research on universe expansion

Looking ahead, the team plans to observe the Coma cluster using JWST. This galaxy cluster is much farther away and offers a chance to bypass supernovae entirely.

If successful, these new measurements will provide another independent value for the Hubble constant.

“These measurements will allow us to measure the Hubble constant directly, without the additional step of needing the supernovae. I am optimistic about resolving this in the next few years, as we boost the accuracy to make these measurements,” said Freedman.

The study is published in The Astrophysical Journal.

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