The James Webb Space Telescope adds to Hubble’s confusing drama
It appears that observations of 10 nearby galaxies by the James Webb Space Telescope point to the Hubble tension – a puzzling discrepancy in measurements regarding the speed of Expansion of the universe – may not be real after all.
The James Webb Space TelescopeAccording to observations, the average value of the Hubble constant (H0), which is crucial for determining the expansion rate of the universe, is 69.96 kilometers per second per megaParsecThis is indeed consistent with predictions from the Standard Model of Cosmology, That should really be the end of the issue. However, the results also highlight a crucial difference of opinion.
In 2013 European Space AgencyThe Planck mission measured the Hubble constant at 67.4 kilometers per second per megaparsec. In other words, this means that each megaparsec (one million parsecs or 3.26 million Light years) expands by 67.4 kilometers 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 are revealed in the light of the cosmic microwave background (CMB) and then applying our standard model of cosmology to predict the expansion rate. Assuming the standard model is correct, this method should have an accuracy of 1%.
In addition, measurements by a team led by Adam Riess of Johns Hopkins University, which Hubble Space Telescope to measure cosmic expansion with Type Ia Supernovathese are the explosions of White Dwarf Stars, disagree. Type Ia supernovae have a standardizable maximum brightness, which means that astronomers can use their brightness to measure how far away they must be. This distance is then multiplied by their Redshiftbecause the faster the universe is expanding, the greater the redshift of an object. This method gives H0 as 73.2 kilometers per second per megaparsec, which means that the universe is expanding faster than the Standard Model predicts. Scientists call this discrepancy the Hubble stress.
Related: The James Webb Space Telescope complicates the paradox of the expanding universe by verifying the work of Hubble
And now new work led by Wendy Freedman of the University of Chicago raises some difficult questions.
Freedman’s team, working on a project called the Chicago–Carnegie–Hubble Program (CCHP), used the JWST to determine the distance to ten relatively nearby Galaxies all of which were Type Ia supernovae. The distance measurements were then verified using 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-How Stars The second method involves something called the asymptotic giant branch of the J region, which refers to a type of red giant star that is rich in carbon and has similar intrinsic infrared brightnesses. The third cross-check was done with Cepheid variables Stars that have a period-luminosity relationship, first discovered by Henrietta Swan Leavitt in 1908, that links the pulsation period to the maximum luminosity. In other words, by simply measuring how long it takes a star to pulsate, we can calculate its maximum brightness and compare that to how bright it is in the Night sky to determine how far away it must be.
The CCHP team measured H0 at 69.85 km/s/Mpc at the tip of the red giant branch and 67.96 km/s/Mpc at the carbon stars. So far, so good – the associated error bars include the Planck measurement of H0 and bring it into good agreement with the Standard model.
However, the Cepheids did not play along. From them, the CCHP team determined a value of 72.04 km/s/Mpc, which does not agree with 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 tension,” Freedman said in a opinion“On the contrary, it looks as if our standard cosmological model for explaining the Evolution of the Universe holds.”
Nevertheless, the measurements of Cepheids still seem to generate tension. Cepheids form the bottom rung of the cosmic distance ladder, followed by Type Ia supernovas, as they are visible 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 measurements of Type Ia supernovas.
However, Freedman has expressed concerns in the past about a potential problem called “overcrowding.” Although the Hubble Space Telescope Although the observatory’s resolution is high enough to identify Cepheid variable stars in other galaxies, it is possible that low-mass stars in close proximity to a Cepheid may not be resolved and may blur in the Cepheid’s light, which may affect the scientific results.
Earlier this year, Riess led a team that used the JWST to review Hubble’s observations of Cepheids and concluded that Crowding was not a problemHowever, Freedman and his colleagues point out in their research that the two methods that least exhibit crowding – the tip of the red giant branch and carbon stars – produce values that are consistent with the Standard Model.
While attention is now focused on measuring galactic distances using Cepheid variables, further measurements with the JWST of galaxies with Type Ia supernovas will be invaluable in confirming the results from these 10 galaxies. However, Type Ia supernovas are relatively rare in galaxies that also have resolvable Cepheids, red giants and carbon stars, meaning it may take some time to Time to obtain a sufficiently large sample.
The results of the CCHP team led by Freedman are currently available as formand were submitted to the Astrophysical Journal for peer review.
