TThe James Webb Space Telescope has confirmed findings from smaller telescopes regarding how fast the universe is expanding. Instead of settling the physics debate, this makes matters worse, because previous measurements contradict what astronomers believe should happen, based on Echoes of the Big Bang. This (probably) does not mean we need to throw away most of what we think we know about cosmology, as some say. Popular articles claimbut it leaves a big problem to solve.
Astronomers have come up with a number of ways to determine how fast the universe is expanding, a measurement that has important implications for the age and future of the universe. Initially, these forecasts came with widespread uncertainties, and while the baseline forecasts varied, the error bars overlapped, so there was little to worry about.
However, as our tools improved and the number of sources studied increased, the discrepancies did not disappear. This is now known as the “Hubble tension,” a reference to the Hubble constant, the number that defines the relationship between the distance of a distant object and its speed.
The James Webb Space Telescope is able to make one of the crucial measurements, the distance to distant galaxies, with greater accuracy than any other instrument. Perhaps, some astronomers thought, it would provide an answer closer to that obtained by other methods, resolving the Hubble tension. Instead, it supported the results from other telescopes.
“Have you ever had trouble seeing a mark that was at the edge of your vision? What does it say? What does it mean? Even with the most powerful telescopes, the ‘marks’ that astronomers want to read look so small that we struggle too,” said Professor Adam Rees of Johns Hopkins University. In a statement. Rees shared the 2011 Nobel Prize in Physics for proving that the expansion of the universe is accelerating.
“The sign that cosmologists want to read is the sign of the cosmic speed limit that tells us how fast the universe is expanding — a number called the Hubble constant,” Rees explained. “Our mark is written in the stars in distant galaxies. The stars in those galaxies tell us how far away they are, and therefore how long that light has traveled to reach us, and the redshifts of the galaxies tell us how much the universe has expanded over that time, and thus tell us the rate of expansion.”
Rees won his prize for helping to make this measurement using Type Ia supernovae, whose peak intrinsic brightness is very consistent. However, this would require waiting for the right type of supernova to explode. Stars known as Cepheid variables provide an alternative, being more abundant.
The brightness of a Cepheid is related to the rate at which it expands and contracts, again giving us a measurement that can be used to calculate the distance between them. Cepheid variables gave us our first idea of the size of the universe, revealing that distant galaxies lie outside the Milky Way.
However, they are not as bright as supernovae, and Cepheid variables cannot be seen in distant galaxies. However, hundreds of millions of light-years away, they can calibrate supernova measurements, providing additional precision, but only if we can distinguish them from nearby ordinary stars.
The James Webb Space Telescope works at wavelengths where this is easier to do than with the Hubble scope, and Reiss and his colleagues have used this to measure more than 320 Cepheid stars, some in the relatively nearby galaxy NGC 4258 and in NGC 5584, which hosted a recent supernova.
Their measurements show that mistrust of Hubble’s accuracy was not unfounded, as it was measuring these galaxies very well. However, what the two space telescopes found doesn’t exactly fit expectations based on the cosmic microwave background.
The Hubble tension remains unresolved.
“The most exciting possibility is that stress is evidence of something we are missing in our understanding of the universe,” Rees added. “This could indicate the existence of exotic dark energy, exotic dark matter, a revision of our understanding of gravity, or the existence of a unique particle or field.” As if ordinary dark energy and dark matter weren’t confusing enough.
Four centuries later, Shakespeare remains right: there is We are More things in heaven and earth than anyone in his philosophy, including Horatio, could dream of.
The study was previously accepted Astrophysical JournalA preview is available at ArXiv.org.
A previous version of this article was published in September 2023
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