The ongoing problem with the universe’s expansion rate may not require rewriting everything we know about physics. New measurements from the James Webb Space Telescope show that the local universe is moving away from us at a rate of about 70 kilometers (about 43 miles) per second per megaparsec.

If true, it would be a major revelation. It could finally resolve a discrepancy between measurements of the universe’s acceleration of expansion that has vexed scientists for most of a century: the Hubble tension, sometimes called the biggest crisis in cosmology.

Much more work will be needed before we can declare this question finally resolved, but the new measurements using three different types of stars could be a significant step forward. The results of the research are published in The Astrophysical Journal and are available on arXiv.

“Based on the new JWST data and using three independent methods, we find no definitive evidence for the existence of the Hubble extension,” says astronomer Wendy Friedman of the University of Chicago. “On the contrary, it appears that our standard cosmological model for explaining the evolution of the universe remains valid.”

The point is, the universe is expanding at an acceleration known as the Hubble constant. To calculate this constant, we can use different types of observations that give their own measurements.

Those observable from the early universe include the cosmic microwave background (remnants of microwave radiation from the first light to penetrate the universe) and baryon acoustic oscillations, patterns in the distribution of distant galaxies consistent with waves that once vibrated in the early universe.

These two signals are known as the standard rulers because we know how big they are. They provide direct, precise measurements of distances, and suggest that the universe is expanding at a rate of about 67.4 kilometers per second per megaparsec.

Signals from the neighboring universe are known as standard candles. These are objects with known intrinsic brightness, such as Cepheid variables and Type Ia supernovae. Because we know how bright they are, we can accurately calculate their distance. And they suggest that the Hubble constant is about 74 kilometers per second per megaparsec.

There are overlapping errors in both types of measurements, so this discrepancy is not the end of cosmology as we know it. But it would be nice to have a more precise number for the expansion rate with confidence. Or, if there is more than one expansion rate, to explain why different parts of the universe expand differently.

Friedman has been working for several years to measure the Hubble constant using methods other than the more traditional standard candles, focusing specifically on stars at the tip of the red giant branch, or TRGB stars.

These stars attain a uniform size and brightness, making them a sensitive tool for measuring the distance to nearby galaxies. Using observations from a variety of instruments, including Hubble and Gaia, Friedman and his colleagues made several measurements of the TRGB, which yielded a Hubble constant of about 69–70 kilometers per second per megaparsec.

Enter the James Webb Space Telescope, the most powerful space telescope ever deployed. Friedman and his team used it to measure TRGB stars, as well as Cepheid variables and a type of carbon-rich giant star that they say is a new type of standard candle, based on its consistent brightness.

By measuring the distances to all three stars independently, the researchers obtained a wealth of data that they could use to cross-check for systematic errors to obtain an independent measurement of the Hubble constant.

For TRGB stars, the researchers obtained a value of 69.85 kilometers per second per megaparsec. For carbon stars, it was 67.96. The Cepheid variables differ slightly at 72.05, but the error ranges for all three overlap.

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

We’re not out of the woods yet. While the measurement is within the margin of error of both standard rulers and standard candles, we’ve been getting different values ​​for too long for the issue to be decided so sharply. In fact, earlier this year, JWST measurements of Cepheid variables and Type Ia supernovae were used to confirm Hubble’s measurement of 73 kilometers per second per megaparsec.

So we’ll need a lot more measurements, re-measurements, and more measurements to be sure. But the new numbers suggest that variables between different observables could still explain the discrepancy without requiring any new theory to be introduced. But who knows? We might even encounter some new physics in our search for an answer. The study was published in The Astrophysical Journal and is available on arXiv.