For years, scientists have puzzled over a strange mismatch in how fast the universe seems to be expanding.
Depending on whether they looked at the early universe or measured today’s galaxies, the numbers didn’t match.
This raised serious questions about whether our current model of the universe—the Standard Model—was missing something big.
Now, thanks to new data from the powerful James Webb Space Telescope, scientists at the University of Chicago say the conflict may not be a problem after all. The results suggest that the Standard Model is still standing strong.
“At the moment, the Hubble Constant doesn’t seem to be the issue,” said Prof. Wendy Freedman, a leading astronomer in this area. The Hubble Constant is the number that tells us how fast the universe is expanding.
There are two main ways to measure the Hubble Constant. One method uses ancient light left over from the Big Bang, called the cosmic microwave background. It tells us about the early universe.
The second method, which Freedman specializes in, involves looking at how galaxies are moving away from us now. That’s much harder to do because it depends on measuring distances very precisely.
To do this, scientists look at special stars that explode as supernovae. If they know how bright these explosions should be, they can compare that to how bright they appear and calculate how far away they are. Freedman also developed two other ways to measure distance, using red giant stars and carbon stars.
However, these methods require many corrections. Light can be dimmed by dust, and stars can vary slightly in brightness over time.
The tools used for measurement can also introduce tiny errors. That’s where the James Webb Space Telescope has made a big difference. It’s four times sharper than the Hubble Telescope and ten times more sensitive, letting scientists see through dust and measure faint stars more accurately.
With the help of Webb, Freedman and her team were able to double the number of galaxies they used to calibrate their data.
Their new measurement of the Hubble Constant—70.4 kilometers per second per megaparsec—now closely matches the value from early-universe data, 67.4. This brings both measurements into agreement for the first time in years.
The results, published in The Astrophysical Journal, offer hope that this long-standing mystery might be close to being solved.
Freedman and her team plan to continue their work with the Webb Telescope, using it to gather even more precise data from a group of galaxies known as the Coma Cluster. “I’m optimistic we’ll have a clear answer in the next few years,” she said.
