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Observations of 10 nearby galaxies with the James Webb Space Telescope appear to point to the Hubble voltage, which is a puzzling discrepancy in measurements of the speed of the expansion of the universe —may not be true after all.
The James Webb Space TelescopeObservations from Earth show that the average value of the Hubble constant (H0), which determines the rate at which the universe expands, is 69.96 kilometers per second per megasecond.parsecThis is indeed consistent with the predictions arising from the Standard Model of cosmology, which should sound like the issue is settled, but the findings also highlight an important disagreement.
In 2013 the European Space AgencyThe ‘s Planck mission measured the Hubble constant at 67.4 kilometers per second per megaparsec. In other words, this means that every megaparsec (one million parsecs, or 3.26 million light years) is expanding by 67.4 kilometers (41.9 miles) every second. The Planck science team was able to derive this value of the Hubble constant by measuring the fundamental properties of the universe that were recorded in the light from the cosmic microwave background (CMB) and then apply our Standard Model of cosmology to predict the expansion rate. Assuming the Standard Model is correct, this method should be accurate to within 1%.
In addition, measurements were taken by a team led by Adam Riess of Johns Hopkins University, who Hubble Space Telescope to measure the cosmic expansion using type Ia supernovaewhich are the explosions of white dwarf stars, disagree. Type Ia supernovae have a standardized peak brightness, meaning astronomers can measure how far away they must be based on how bright they appear. This distance is then compared to their redshiftbecause the faster the universe expands, the greater the redshift of an object. That method sets H0 at 73.2 kilometers per second per megaparsec, implying that the universe is expanding faster than the standard model predicts. It is this disagreement that scientists call the Hubble voltage.
Related: James Webb Space Telescope complicates expanding universe paradox by verifying Hubble work
And now new research led by Wendy Freedman of the University of Chicago raises some tough questions.
Freedman’s team, working on a project called the Chicago–Carnegie–Hubble Program (CCHP), used the JWST to measure the distances to 10 relatively nearby planets. galaxies all of which were observed to have had a Type Ia supernova. The distance measurements were then checked by three independent means.
The first of these three independent methods is known as the “tip of the red giant branch”, which describes the maximum brightness that developed Sun-like stars red giants. The second method involves something called the J-region asymptotic giant branch, which refers to a flavor of red giant stars that are rich in carbon and have similar intrinsic infrared luminosities. The third cross-check was performed using Cepheid variable stars, which have a period-luminosity relationship first discovered by Henrietta Swan Leavitt in 1908, which links the period of pulsation to maximum luminosity. In other words, by simply measuring how long a star takes to pulsate, we can calculate what its maximum brightness should be and compare that to how bright it appears in the night sky to deduce how far it should be.
The CCHP team measured H0 as 69.85 km/s/Mpc using the top of the red giant branch, and they measured 67.96 km/s/Mpc using the carbon stars. So far, so good — the associated error bars include the Planck measurement of H0, so they are in good agreement with the standard model.
The Cepheid variables, however, played no role. The CCHP team based this on a value of 72.04 km/s/Mpc, which does not match the other measurements. Together, the four methods give an average value of 69.96 km/s/Mpc.
“Based on these new JWST data and using three independent methods, we find no strong evidence for a Hubble voltage,” Freedman said in a proposition“On the contrary, it appears that our standard cosmological model for explaining the evolution of the universe stand firm.”
Still, the Cepheid variable measurements seem to be exciting. Cepheids are the lowest rung of the cosmic distance ladder, with Type Ia supernovae the next rung up because they are seen at greater distances than Cepheids. In the work of Riess’ group — Supernova H0 for the Equation of State, or SH0ES for short — Cepheids are crucial for calibrating the Type Ia supernova measurements.
However, Freedman has expressed concerns in the past about a potential problem called “crowding.” Although the Hubble Space Telescope Although the resolution is high enough to identify Cepheid variable stars in other galaxies, low-mass stars very close to a Cepheid may not be resolved well and may therefore fade away in the light of the Cepheid, affecting the scientific results.
Earlier this year, Riess led a team that used the JWST to check Hubble’s observations of Cepheids and concluded that crowds were not a problemHowever, in their research paper, Freedman and fellow researchers point out that the two methods least affected by crowding — the top of the red giant branch and the carbon stars — produce values consistent with the Standard Model.
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— ‘Hubble problem’ could grow with new measurement of universe’s expansion
— Could a ‘supervoid’ end the ongoing debate about the expansion rate of the universe?
— The expansion of the universe could be a mirage, a new theoretical study suggests
While the focus will now be on galactic distance measurements using Cepheid variables, more measurements using the JWST of galaxies with Type Ia supernovae will be invaluable in confirming the results for these 10 galaxies. However, Type Ia supernovae in galaxies that also have resolvable Cepheid variables, red giants, and carbon stars are relatively rare, meaning that it may take some time time to get a large enough sample.
The results of the CCHP team led by Freedman are currently available as preprintand have been submitted for peer review to The Astrophysical Journal.