An article accepted for publication in “The Astrophysical Journal” reports the results of calculating the universe’s expansion rate based on the observation of Cepheids with the James Webb Space Telescope. In particular, a team of researchers led by Adam Riess used the NIRCam instrument to observe over 330 cepheids in the galaxies NGC 4258 and NGC 5584. The results are more precise than those obtained in the past with the Hubble Space Telescope but confirm the accuracy of the previous calculation of the universe’s expansion rate. This leaves open the question of the difference in results obtained with different methods.
The image (NASA, ESA, CSA, Adam G. Riess (JHU, STScI). Illustration: Joyce Kang (STScI)) shows a diagram illustrating the combined power of the James Webb and Hubble space telescopes in studying Cepheids present in the galaxy NGC 5584 with the NIRCam (Near-Infrared Camera) and WFC3 (Wide Field Camera 3) instruments, respectively. Stars close to Cepheids can interfere with detections with their light, and from this point of view, Webb allows for more precise detections, with less “noise” generated by those stars.
For years, many astronomers have been trying to get a precise measurement of the universe’s expansion rate. The issue became more complicated and more important after studies started concluding that the expansion is accelerating. Everyone expected that the expansion was slowing down due to the gravity generated by all the matter existing in the universe, so it was a truly surprising discovery. Adam Riess was among the winners of the Nobel Prize for Physics in 2011 for his contribution to this discovery and is continuing to work on the problem.
Different calculation methods have been used to estimate the universe’s expansion rate and what was called a tension in the world of physics is due to the significant differences between the results obtained. One of the calculation methods is based on what are called standard candles, variable stars called Cepheid variables that have a very close correlation between their variability period and their absolute brightness. In particular, the difference between the results obtained from the study of Cepheids with the Hubble Space Telescope is too great from that obtained from the examination of the cosmic microwave background radiation.
The James Webb Space Telescope is a major step forward over Hubble and is capable of obtaining more precise information about Cepheids. However, the results of processing that information confirms past calculations. Someone suspected that there could be some systematic error in the measurements obtained with Hubble but the confirmations obtained with Webb, which is very different and more accurate, eliminated this hypothesis. Obtaining measurements with different instruments and repeating them every time a new instrument becomes available is crucial for this type of verification.
The hypothesis of dark energy as the cause of the acceleration of the expansion of the universe could also somehow concern the differences between the measurements. At the moment these are speculations, which sometimes also include dark matter, another of the great current cosmological mysteries. A revision of our understanding of the force of gravity represents an alternative explanation embraced by some scientists. Recently, some tests of this type of model gave interesting results but are still far too limited to confirm it.
Cosmological studies conducted with the James Webb Space Telescope have just begun and the scientific mission of the Euclid Space Telescope, designed to investigate these astronomical mysteries and launched on July 1, 2023, has yet to begin. These studies require a lot of work and patience but the stake is the discovery of the secrets of the universe.