Sometimes scientists get different results when they measure things differently. Whenever that happens with something as crucial to the long-term future of humanity as the rate of expansion of the universe, it can attract a lot of attention. For decades, scientists have thought there was such a difference, known as the Hubble voltage, in measurements of the rate at which the universe is expanding. But a new paper by researchers at the University of Chicago and the Carnegie Institution for Science, using data from the James Webb Space Telescope (JWST), suggests there is no difference at all.
To better understand this, let's first look at the Hubble stress. Edwin Hubble, the namesake of the Hubble Space Telescope, the predecessor to the JWST, first discovered the expansion of the universe when he studied the speed at which galaxies move. He found that galaxies farther away from us traveled faster than those closest to us, and the best answer we have as to why this is the case is that the universe itself is expanding.
While this doesn't happen on a scale that we would notice in our everyday lives, at the scale of the space between galaxies, it is definitely noticeable, and in a number of ways. Historically, there have been two different ways to measure this Hubble constant, as the expansion rate is called. One of these involved studying the cosmic microwave background (CMB) radiation, and another involved looking at the speed of galaxies, as Hubble did.
Fraser discusses the impact of JWST on Hubble voltage ahead of publication of latest paper
Data on the CMB have long been consistent and precise. Studies have shown that it indicates an expansion rate of 67.5 kilometers per second per megaparsec. To put that in perspective, the universe is adding a little less than an hour to highway travel time every second, but this is happening on a scale of 3.2 million light years. Again, this expansion is imperceptible on our own scale, but it is very much perceptible on the immense scales of the universe.
However, the calculations of this expansion value differ in the second method of measuring galaxies. Traditionally, the value is about 9% higher and is estimated at 74 kilometers per second per megaparsec. This measurement is usually made using data from two different types of stars in these distant and nearby galaxies – Cepheids and “tip of the red giant branch”.
Dr. Wendy Freedman, one of the paper's authors, is an expert in using Cepheids to measure the distance of objects, so the opportunity to use JWST's even more precise instruments was probably a great moment for her and her team. But they didn't stop there. They added data from another type of star whose use to calculate the distance to an object has become more popular recently. Carbon stars are known for their constant brightness and near-infrared wavelengths—the very wavelengths that JWST was designed to study. Using these known properties, the researchers were able to calculate redshift and other variables, allowing them to use this new technique to validate their version of the Hubble constant.
As Fraser explains in this video, measuring distances is difficult from an astronomical perspective.
The number they obtained was much closer to the number calculated using the CMB method – 70 kilometers per second per megaparsec, a difference of only 3.5%. This is within the limits of estimates for most astronomical calculations, so the authors suggest that there may be no contradiction between the two measurements.
This claim will undoubtedly cause controversy in the astronomical community, as there are several theories with numerous proponents that explain the differences in measurements. But as instruments like the JWST provide increasingly detailed data and researchers get better at constraining some of the astronomically large values, we may one day prove that this existential crisis that has been at the center of cosmology for decades may never have existed.
Learn more:
University of Chicago – New data from the Webb telescope suggest that our model of the universe may hold up after all
Freedman et al. – Status report on the Chicago-Carnegie Hubble Program (CCHP): Three independent astrophysical determinations of the Hubble constant with the James Webb Space Telescope
UT – Astronomers rule out an explanation for the Hubble tension
UT – If our part of the universe is less dense, would that explain the Hubble voltage?
Cover image:
Using new data from the James Webb Space Telescope, scientists have made new measurements of the rate at which the universe is expanding over time. To do so, they measured the light from ten galaxies, including the galaxy known above as NGC 3972.
Source: Yuval Harpaz, data via JWST
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