Earlier this year, JWST researchers reported on measurements that built on last year's confirmation from Webb data that Hubble's expansion rate measurements were accurate, at least for the first few “rungs” of the “cosmic distance ladder.” But there was still the possibility of undiscovered errors that could increase as one looked deeper into the universe (and therefore further back in time), especially for brightness measurements of more distant stars.
Three views of NGC 4258 (Messier 106). The left and middle images show the galaxy in visible light, while the right image of the JWST is in infrared.
Credit: ESA/WEBB, NASA & CSA
Additional observations of variable Cepheid stars – 1,000 in total in five host galaxies out to 130 million light-years away – correlated with the Hubble data helped JWST see past the interstellar dust that has made Hubble's own images of those stars blurrier and more overlapping. This allowed astronomers to more easily distinguish between individual stars. These results further confirmed the accuracy of the Hubble data and allowed astronomers to rule out measurement errors with a high degree of confidence.
A critical cross-check
This latest study serves as a critical check on the April paper, using three different measurements to determine the distances to galaxies known to host supernovae. “Comparing Hubble may sound prosaic, but the Hubble results reveal a profound tension in the universe between how fast it is expanding now (as measured by Hubble) versus the prediction of the Standard Model, LambdaCDM (calibrated by the Cosmic Microwave Background),” lead author Adam Riess of the Space Science Telescope Institute at Johns Hopkins University told Ars. “So Webb's confirmation of Hubble means we're really seeing something wrong with it universe.”
The new study, which includes data from two independent groups working to refine the Hubble constant, includes about a third of the entire sample of galaxies collected by Hubble. The authors used the distance to the galaxy NGC-4258 (also known as Messier 106) as a reference point, since that distance is known. They used pulsating stars, known as Cepheid variables, to calculate distances and checked their work with complementary distance measurements based on carbon-rich stars and red giants. They ended up with a Hubble constant value of 72.6 km/s/Mpc, very close to Hubble's value of 72.8 km/s/Mpc.
