Hubble’s law is considered the 1st observational basis for the expansion ofour universe, thanks to Edwin Hubble, who was the first to calculate the constant from his measurements of stars in the 1920s. What he found was absolutely remarkable: all of the galaxies in the universe appeared to be moving away from our planet. Furthermore, the farther a galaxy was, the faster it was receding. Generations of astronomers have improved upon Hubble’s original methods and with time developed the new ones.
Image credits:ESA / Hubble
More info:APS
Wendy Freedman and her colleagues have used the James Webb Space Telescope (JWST) to add two more methods to the local distance ladder. The team were observing 2 other type ofstars– carbon stars and red giant branch ones. Each of them had predictable luminosities based on their mass.
Wendy Freedman presented her study on the 6th of April at a meeting of the American Physical Society: “These much more precise data are not screaming out saying you really need new physics. We are finally converging now – it’s really exciting,” the scientist couldn’t hold back her joy.
This method is called blind analysis because in the beginning, you don’t see any real numbers, nor any real values until the very end. Only when it’s clear that it’s working can the scientists input the real data, a process called unblinding – when you finally get to see the real results.
Our universe is expanding, yet 2 different main ways to measure it until now have resulted in different answers
Image credits:APS
Image credits:ESO
Image credits:NOIRLab
It’s important to mention that the scientific team not only carried out a blind analysis, but also completely reanalyzed all of the old Hubble Space Telescope data as well. After doing all of it, they have found that all the 3 different types of stars they used agreed on the distances to those neighboring galaxies, which meant that the data is consistent. And then they could recalibrate the distances to those in more distant galaxies with the supernova and then recalculate the current expansion rate of the universe. Thescientistsgot a Hubble constant of about 69 km/sec/Mpc, which is consistent with the CMB measurements. “The difference between a Hubble constant of 73 and 69 is small, but these things are really important to get right,” said Freedman.
Some other scientists are skeptical about this new discovery. Daniel Scolnic, from Duke University in North Carolina, states that the number of galaxies observed with JWST is relatively small and that the other groups have come up with a higher figure for the Hubble constant based on JWST data, rather than the lower one Freedman’s team found.
Adam Riess, from Johns Hopkins University in Maryland, also looks at the new study carefully: “I do not believe the Hubble tension has changed, but I do know there isa differencein the way we are analyzing supernovae… one that produces a difference in the Hubble constant. I don’t think it would be fair or accurate to define the size of the tension from the lowest (or highest) measure.”
For the past decade, astrophysics have divided into 2 groups: the one that believes that the difference is significant and the 2nd one that thinks it could be due to errors in measurements
Image credits:NASA
The Hubble constant has seemed to be an unsolvable puzzle for many years. Therefore, according to Daniel Scolnic, if the Hubble tension finally disappeared, it would mean passing the ‘end-to-end’ test of cosmology. Even though Wendy Freedman and her colleagues still have to do more calculations tobetterprove their statement, to be so close to nailing down the most controversial numbers in cosmology for years is already a very huge accomplishment.
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