The universe is expanding – but astronomers do not agree on the rate of this expansion. NASA’s famous observatory, the James Webb Space Telescope, confirmed that there is a problem with our understanding of the expansion of the universe. James Webb’s new measurements are the most accurate of their kind, but they do not eliminate the confusion between the two ways scientists track this expansion.
A historical look at the expansion
In 1929, astronomer Edwin Hubble discovered that all galaxies we see are moving away from us. The relationship between the distance to a galaxy and its rate of motion is now known as “Hubble’s Law.” This same constant law is used to describe the expansion rate of the universe. It also tells us how old the universe is: astronomers can use the Hubble constant to “turn back time” to where the universe becomes a single point in space – the Big Bang.
Methods of measuring the fundamental number of the expansion of the universe
There are two main ways to measure this key number. The first is to track small fluctuations in the cosmic microwave background from the beginning of the universe. The second is to watch the flashing stars known as Cepheid stars. But these two methods differ. This mysterious discrepancy is known as “Hubble tension,” and it is not clear whether this is a problem in our models of the universe or in our measurements.
What are Cepheid stars and how can we benefit from them?
If our problem is with the measurements, the error may be due to the way we scan the Cepheid stars. Astronomers consider these objects to be a kind of “standard candles,” objects in space whose intrinsic brightness is known. We can observe how bright one of these stars is in the sky. If it’s faded, it’s further away. If it’s brighter, it’s closer.
Researchers use the brightness of these stars like a ruler to measure distance. Then, using methods such as spectroscopy, they can estimate the motion of distant galaxies. Combining these observations tells us the expansion rate of the universe.
“When we use Cepheid stars like this, we have to be very sure that we measure their brightness correctly, otherwise our distance measurements will be inaccurate,” explains astronomer Tarini Konchadi, a program officer at the National Academies of Sciences, Engineering, and Medicine. “However, cepheid stars could be in star-packed places in their galaxies, and if our telescopes are not sensitive enough, we cannot clearly distinguish between a cepheid star and the stars surrounding it.”
The difference between Hubble and James Webb
Before James Webb, the best measurements of Cepheid stars were made by the Hubble Space Telescope. The Hubble Telescope couldn’t distinguish individual cepheid stars because they were clustered in crowded regions, but James Webb could — and just now. James Webb looked at two distant galaxies and made measurements of the Hubble Constant 2.5 times better than the Hubble Telescope could provide.
“Webb’s measurements have significantly reduced noise in measurements of Cepheid stars,” Adam Reiss, project leader and astronomer at Johns Hopkins University, said in a NASA press release. “This kind of improvement is what astronomers dream of!”
One of James Webb’s main advantages is its ability to peer into the universe with infrared light, which helps penetrate the dust between our telescopes and the Cepheid stars. “Sharp infrared vision is one of the strengths of the James Webb Space Telescope,” Rees said.
What did the results show?
However, the new results from James Webb showed a match with those from the Hubble Telescope, but with smaller errors – so we can’t pin the confusion on those old numbers.
Reiss and his team’s new results are just the beginning, and they still have many more galaxies to observe with GEMS Webb. “I think the court is still out on whether James Webb has completely eliminated the crowding problem as a solution to the Hubble jitter,” says University of Chicago astronomer Abigail Lee. “Data analysis for the remaining 42 galaxies [التي تخطط جيمس ويب لمراقبتها] “It will reveal whether the Hubble tension is alive and real or whether there are actual errors in measurements of Cepheid stars.”
What awaits the future of the universe?
The fate of the universe, or at least the Hubble tension, does not depend solely on James Webb. Several other facilities will come into service over the next few years, providing further evidence of this research. For example, the Vera Rubin Observatory will scan the entire southern sky every several nights when it opens next year, and will likely discover many additional Cepheid stars.
“We are at a point where astronomers have to be overwhelmed with the most sensitive and large-scale data yet,” says Tarini Konchadi. There may not be a clear answer yet, but astronomers are certainly on the lookout for a solution to this mystery.
