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<\/p>\nExpansion of the Universe: An End to the \u2018Hubble Tension\u2019?
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When one set of data fails to agree with another over the same phenomenon, things can get interesting. It\u2019s in such inconsistencies that interesting new discoveries are sometimes made, and when the inconsistency involves the expansion of the universe, there are plenty of reasons to resolve the problem. Lately the speed of the expansion has been at issue given the discrepancy between measurements of the cosmic microwave background and estimates based on Type Ia supernovae. The result: The so-called Hubble Tension.<\/p>\n
It\u2019s worth recalling that it was a century ago that Edwin Hubble measured extragalactic distances by using Cepheid variables in the galaxy NGC 6822. The measurements were necessarily rough because they were complicated by everything from interstellar dust effects to lack of the necessary resolution, so that the Hubble constant was not known to better than a factor of 2. Refinements in instruments tightened up the constant considerably as work progressed over the decades, but the question of how well astronomers had overcome the conflict with the microwave background results remained.<\/p>\n
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Now we have new work that looks at the rate of expansion using data from the James Webb Space Telescope, doubling the sample of galaxies used to calibrate the supernovae results. The paper\u2019s lead author, Wendy Freedman of the University of Chicago, argues that the JWST results resolve the tension. With Hubble data included in the analysis as well, Freedman calculates a Hubble value of 70.4 kilometers per second per megaparsec, plus or minus 3%. This result brings the supernovae results into statistical agreement with recent cosmic microwave background data showing 67.4, plus or minus 0.7%.<\/p>\n
Image:<\/strong> The University of Chicago\u2019s Freedman, a key player in the ongoing debate over the value of the Hubble Constant. Credit: University of Chicago.<\/p>\n While the cosmic microwave background tells us about conditions early in the universe\u2019s expansion, Freedman\u2019s work on supernovae is aimed at pinning down how fast the universe is expanding in the present, which demands accurate measurements of interstellar distances. Knowing the maximum brightness of supernovae allows the use of their apparent luminosities to calculate their distance. Type 1a supernovae are consistent in brightness at their peak, making them, like the Cepheid variables Hubble used, helpful \u2018standard candles.\u2019<\/p>\n The same factors that plagued Hubble, such as the effect of dimming from interstellar dust and other factors that affect luminosity, have to be accounted for, but JWST has four times the resolution of the Hubble Space Telescope, and is roughly 10 times as sensitive, making its measurements a new gold standard. Co-author Taylor Hoyt (Lawrence Berkeley Laboratory) notes the result:<\/p>\n \u201cWe\u2019re really seeing how fantastic the James Webb Space Telescope is for accurately measuring distances to galaxies. Using its infrared detectors, we can see through dust that has historically plagued accurate measurement of distances, and we can measure with much greater accuracy the brightnesses of stars.\u201d<\/p>\n<\/blockquote>\n Image:<\/strong> Scientists have made a new calculation of the speed at which the universe is expanding, using the data taken by the powerful new James Webb Space Telescope on multiple galaxies. Above, Webb\u2019s image of one such galaxy, known as NGC 1365. Credit: NASA, ESA, CSA, Janice Lee (NOIRLab), Alyssa Pagan (STScI).<\/p>\n A lack of agreement between the CMB findings and the supernovae data could have been pointing to interesting new physics, but according to this work, the Standard Model of the universe holds up. In a way, that\u2019s too bad for using the discrepancy to probe into mysterious phenomena like dark energy and dark matter, but it seems we\u2019ll have to be looking elsewhere for answers to their origin. Ahead for Freedman and team are new measurements of the Coma cluster that Freedman suggests could fully resolve the matter within years. <\/p>\n As the paper notes:<\/p>\n \nWhile our results show consistency with \u039bCDM (the Standard Model), continued improvement to the local distance scale is essential for further reducing both systematic and statistical uncertainties.<\/p>\n<\/blockquote>\n The paper is Freedman et al., \u201cStatus Report on the Chicago-Carnegie Hubble Program (CCHP): Measurement of the Hubble Constant Using the Hubble and James Webb Space Telescopes,\u201d The Astrophysical Journal<\/em> Vol. 985, No 2 (27 May 2025), 203 (full text<\/a>). <\/p>\n\n
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