With Webb’s help, astronomers verified previous Hubble telescope measurements of the expansion of the universe. It is striking that both space telescopes reached the same result. So the mystery of the Hubble constant remains unsolved.
Astronomers have been trying to figure out how fast the universe is expanding for years. They use the Hubble constant for this purpose; The cosmological parameter that determines the absolute scale, size and age of the universe. It is one of the most direct ways to learn how the universe evolved. However, there is a stark discrepancy between the value of the constant measured by a wide range of independent distance indices and the value expected from the afterglow of the Big Bang. Thus, hopes were placed on the powerful James Webb Telescope to uncover this mystery.
Back to the beginning. Therefore, the Hubble constant is an important parameter in cosmology that describes the rate at which the universe is expanding. But researchers still can’t put their finger on it. This is because it is still not possible to determine the exact value of the Hubble constant. While several methods have already been tried to measure this. One common method is to observe Cepheid stars (pulsars) and supernovae. This indicates that the universe is expanding at a rate of 74 kilometers per second per million parsecs. Another way is to make measurements of the cosmic microwave background radiation from the early universe. Data from the Planck satellite on cosmic background radiation reveal that our universe is expanding at a rate of 67.4 kilometers per second per million parsecs. A difference of six or seven kilometers per second!
It is no coincidence that astronomers look at Cepheids. The brightness of some stars in distant galaxies tells us how far away they are, and thus how long this light has traveled to reach us. The redshift of galaxies tells us how much the universe expanded during that period, and thus reveals the rate of expansion. Cepheid stars give us an accurate measure of distance because these stars are so bright: they are supergiants, 100,000 times brighter than our Sun. In addition, they pulse for several weeks. The longer this period, the brighter it is. Therefore, it is the golden tool for measuring distances between galaxies a hundred million light-years or more away, which is a crucial step in determining the Hubble constant. Unfortunately, stars in distant galaxies are often close together from our point of view, and it is not yet possible to distinguish them well from their “closer” neighbors.
This was one of the reasons for building the Hubble Space Telescope. Before Hubble’s launch in 1990 and subsequent Cepheid measurements, the expansion rate of the universe was so uncertain that astronomers were not even sure whether the universe had been expanding for 10 billion or 20 billion years. Thanks to Hubble, which operates from space and is therefore not affected by the effects of the Earth’s atmosphere, we get a much better picture of this. Hubble can distinguish between individual Cepheid stars in galaxies more than 100 million light-years away, and can measure the period over which these stars change in brightness.
However, Hubble’s measurements left much to be desired. This is because Hubble cannot look properly through the dust that stands between us and the Cepheid stars. Dust absorbs and scatters blue optical light, making distant objects appear faint. This makes it seem further away than it actually is. Unfortunately, Hubble sees less clearly in red light than in blue light, causing the light from Cepheid to mix with other stars in its field of view. But this deficiency was remedied with the arrival of James Webb.
The James Webb Space Telescope is very powerful at detecting infrared light. This telescope is specifically designed to operate in the infrared portion of the electromagnetic spectrum, and contains several instruments that can detect and analyze infrared radiation. Thanks to its large mirror and sensitive optics, the telescope can easily separate light from Cepheid stars from nearby stars.
Webb’s observations in the infrared led to measurements of Cepheid stars with much less noise than in the case of Hubble. “This is the improvement that astronomers dream of,” the researchers wrote in a statement. In all, they observed more than 320 Cepheids. This has now led to an amazing result. “We found that previous Hubble measurements were generally correct,” the researchers said. “We also observed four other galaxies using the Webb telescope, which also produced similar results.”
Results This means that measurements of Cepheid stars – and thus the expansion rate of the universe – are at least accurate, as two independent telescopes have reached similar results. But this does not solve the puzzle regarding the exact value of the Hubble constant. “What the results have not yet explained is why the universe is expanding at such a rapid rate,” the statement said. “We can predict the expansion rate of the universe by observing its nascent image, the cosmic background radiation. Then we use our best model of how the universe grows over time to figure out how fast it should be expanding today. The fact that the current measurement of the expansion rate is much higher than expected is a problem.” It has now been going on for a decade. This means that there is something wrong with the universe, or that we are missing something in our understanding of the universe.
To be sure, the last word on the Hubble Constant has not yet been said. Astronomers are now investigating a number of possibilities that could explain this persistent discrepancy. “This could indicate the presence of exotic dark energy, exotic dark matter, a revision in our understanding of gravity or the existence of a unique particle,” the researchers summarized. “The most mundane explanation is that measurement errors are to blame. But new measurements by Webb now show that there may have been no measurement errors when observing Cepheids. So the most interesting options remain on the table for now.”
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