Webb validates Hubble's universe expansion rate measurements

However, the mystery appears to have further deepened. 

The brightness observation of Cepheid variable stars

A team of astronomers from Johns Hopkins University and the Space Telescope Science Institute used this space observatory to estimate the rate at which the universe is expanding. 

As per the official release, the Webb results fall in line with the Hubble Space Telescope findings.

So far, scientists have used a variety of methods to quantify the expansion rate, but the findings have varied. 

Some approaches for estimating universe expansion rely on residual radiation from the early cosmos, such as the cosmic microwave background or a baryon acoustic oscillation (BAO). 

Another method is to calculate distances to objects with well-known intrinsic brightness, such as Type Ia supernovae or Cepheid variable stars.

The authors mention that these types of stars have provided the most “precise measurements of distance for over a century” due to their exceptional brightness.

"[Cepheid variables] are the gold standard tool for the purpose of measuring the distances of galaxies a hundred million or more light years away, a crucial step to determine the Hubble constant. Unfortunately, stars in galaxies are crowded together in a small space from our distant vantage point and so we often lack the resolution to separate them from their line-of-sight neighbors," explained Adam Riess, astrophysicist and a Nobel Laureate, in an official release.  

And the Hubble space telescope has relied on Cepheid variables to measure the expansion using its visible-wavelength resolution abilities. 

"Hubble has better visible-wavelength resolution than any ground-based telescope because it sits above the blurring effects of Earth's atmosphere. As a result, it can identify individual Cepheid variables in galaxies that are more than a hundred million light-years away and measure the time interval over which they change their brightness,” added Riess.

Riess also mentioned that before the launch of Hubble in 1990 and its subsequent measurements using Cepheid variables, the rate of the universe's expansion was characterized by significant uncertainty.

Webb confirms Hubble's observations 

To begin, the scientists used Webb to examine a galaxy with a known distance. This initial observation aided in calibrating the telescope to the brightness of Cepheid variables. 

Following that, Webb observed Cepheids in additional galaxies, amassing a total of 320 star observations. The data from the Webb telescope validates the precision of three decades of Hubble observations of Cepheid variables.

“We confirmed that the earlier Hubble Space Telescope measurements were accurate, albeit noisier,” Riess added.

The cause of this tension remains elusive, but one of the leading candidates is dark energy, a hypothetical kind of energy that is thought to pervade all of space and is responsible for the universe's accelerating expansion.

"With Webb confirming the measurements from Hubble, the Webb measurements provide the strongest evidence yet that systematic errors in Hubble's Cepheid photometry do not play a significant role in the present Hubble tension," Riess mentioned.

"As a result, the more interesting possibilities remain on the table and the mystery of the tension deepens."

The study is accepted for publication in The Astrophysical Journal. The results can be accessed on arXiv.

Study abstract:

High-resolution JWST observations can test confusion-limited HST observations for a photometric bias that could affect extragalactic Cepheids and the determination of the Hubble constant. We present JWST NIRCAM observations in two epochs and three filters of >330 Cepheids in NGC4258 (which has a 1.5% maser-based geometric distance) and in NGC5584 (host of SNIa 2007af), near the median distance of the SH0ES HST SNIa host sample and with the best leverage among them to detect such a bias. JWST provides far superior source separation from line-of-sight companions than HST in the NIR to largely negate confusion or crowding noise at these wavelengths, where extinction is minimal. The result is a remarkable >2.5x reduction in the dispersion of the Cepheid P-L relations, from 0.45 to 0.17 mag, improving individual Cepheid precision from 20% to 7%. Two-epoch photometry confirmed identifications, tested JWST photometric stability, and constrained Cepheid phases. The P-L relation intercepts are in very good agreement, with differences (JWST-HST) of 0.00+/-0.03 and 0.02+/-0.03 mag for NGC4258 and NGC5584, respectively. The difference in the determination of H_0 between HST and JWST from these intercepts is 0.02+/-0.04 mag, insensitive to JWST zeropoints or count-rate non-linearity thanks to error cancellation between rungs. We explore a broad range of analysis variants (including passband combinations, phase corrections, measured detector offsets, and crowding levels) indicating robust baseline results. These observations provide the strongest evidence yet that systematic errors in HST Cepheid photometry do not play a significant role in the present Hubble Tension. Upcoming JWST observations of >12 SNIa hosts should further refine the local measurement of the Hubble constant.