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Observations by the James Webb Space Telescope of 10 nearby galaxies appear to suggest the Hubble stretch, a puzzling discrepancy in measurements of the galaxy’s velocity. expansion of the universe — may not be true after all.
The James Webb Space Telescope‘s observations revealed an average value of the Hubble constant (H0), which plays a key role in determining the expansion rate of the universe, of 69.96 kilometers per second per megahertz.parsecThis is consistent with predictions from the standard model. cosmology, While this might seem like the end of the matter, the findings also highlight a critical disagreement.
In 2013, European Space AgencyThe Planck mission measured the Hubble constant as 67.4 kilometers per second per megaparsec. In other words, this means that each megaparsec (one million parsecs, or 3.26 million light year) is expanding at a rate of 67.4 kilometers (41.9 miles) every second. The Planck team was able to derive this value of the Hubble constant by measuring fundamental features of the universe captured in its light. cosmic microwave background (CMB) and then apply our standard model of cosmology to estimate the expansion rate. Assuming the standard model is correct, this method should be accurate to 1%.
Additionally, measurements made by a team led by Adam Riess from Johns Hopkins University, Hubble Space Telescope measuring cosmic expansion using type Ia SupernovasWhich are the explosions? White dwarf stars try to be different. Type Ia supernovae have a standardizable maximum brightness, which means that astronomers can measure how far away they must be based on how bright they appear. This distance is then redshiftbecause the faster the universe is expanding, the greater the redshift of an object. This method puts H0 at 73.2 kilometers per second per megaparsec, meaning the universe is expanding faster than the standard model predicts. This disagreement is what scientists call the Hubble tension.
Relating to: James Webb Space Telescope complicates expanding universe paradox by checking Hubble’s work
And now, a new study led by Wendy Freedman of the University of Chicago raises some tough questions.
Working on a project called the Chicago-Carnegie-Hubble Program (CCHP), Freedman’s team used JWST to measure the distance to ten relatively nearby locations galaxies All were observed to have type Ia supernova formation. The distance measurements were then cross-checked with three independent instruments.
The first of these three independent methods is known as the “tip” red giant The “branch” defines the evolving maximum brightness sun-like stars so-called red giants can reach. The second method involves something called the J-region asymptotic giant branch, which refers to a type of red giant star that is carbon-rich and has similar intrinsic infrared luminosities. The third cross-check, Cepheid variable Stars that have a period-luminosity relationship, which relates the period of a star’s pulsation to its maximum brightness, first discovered by Henrietta Swan Leavitt in 1908. In other words, by measuring how long it takes for a star to pulsate, we can calculate what its maximum brightness should be, and use this to calculate night sky to work out how far away it needs to be.
The CCHP team measured H0 as 69.85 km/s/Mpc using the tip of the red giant branch, and 67.96 km/s/Mpc using carbon stars. So far so good — the associated error bars cover the Planck measurement of H0, showing standard model.
But Cepheid variables weren’t playing tricks. From these, the CCHP team arrived at a value of 72.04 km/s/Mpc, which doesn’t agree with other measurements. Taken 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 found no strong evidence of a Hubble stretch,” Freedman said. expression“On the contrary, it is similar to the standard cosmological model that we use to explain the universe. evolution of the universe “it depends.”
Still, Cepheid variable measurements appear to continue to be a stretch. Cepheids are at the bottom of the cosmic distance ladder, while type Ia supernovae are the next rung up because they can be seen from greater distances than Cepheids. In Riess’s group’s work—the Equation of State for Supernova H0, or SH0ES for short—Cepheids are critical for calibrating type Ia supernova measurements.
But Freedman has expressed concerns in the past about a potential problem called “crowding.” Hubble Space Telescope Although it has a resolution strong enough to detect Cepheid variable stars in other galaxies, it is possible that low-mass stars very close to a Cepheid may not be resolved and may be blurred by light from the Cepheid, affecting scientific results.
Earlier this year, Riess led a team that used JWST to double-check Hubble’s Cepheid observations, concluding: Crowding was not a problemHowever, Freedman and his colleagues point out in their research paper that the two methods least affected by crowding (the tip of the red giant branch and carbon stars) give values that are in line with the standard model.
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While attention is now focused on measuring galactic distances using Cepheid variables, further measurements with JWST of galaxies with type Ia supernovae will be invaluable in confirming the results from these 10 galaxies. However, type Ia supernovae in galaxies that also contain resolvable Cepheids, red giants, and carbon stars are relatively rare, meaning that it may take some time. time to obtain a sufficiently large sample.
The results from the CCHP team led by Freedman are now available as follows: preprintand has been submitted for peer review in The Astrophysical Journal.