The James Webb Space Telescope (JWST) examined the work of its bigger sibling, the Hubble Space Telescope. Hubble's measurements of the universe's expansion rate are perfect, the pioneering observatory has found, further escalating the so-called “Hubble tension“.
Quite simply, it measures the expansion rate of the universe, which is determined by a property called… Hubble constantjust don't add up.
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Hand notes Cosmic microwave background (CMB) radiation, which resembles a modern picture of the universe only 379,000 years after its appearance. the great explosionAssume that the universe should be expanding today at a rate of about 67.8 kilometers per second per million parsecs. This means that every volume of space is one million A parsec (3.26 million Light year) should be expanding at a rate of 67.8 kilometers (42.1 miles) per second.
An alternative way to measure this expansion is to go up the cosmic distance ladder, with each rung shaped by a different astrophysical landmark such as Cepheid variable stars and Type Ia stars. Supernovae. How bright these objects are can tell us their distances, which we can then compare them with Redshift Values to determine how much the universe expands as its light travels to us. But the problem is that this method gives us a completely different value for the Hubble constant: about 73.2 kilometers (45.5 miles) per second per megaparsec.
The apparent discrepancy between the two measurements is what cosmologists have begun to call the Hubble tension. No one knows why this is, but some hypotheses call for new physics to explain the apparent paradox.
One possible explanation is that there is a measurement error at the bottom rung of the cosmic distance scale, which is home to Cepheid variables. These are stars with a luminosity that fluctuates predictably as the stars pulsate in and out of them. The longer the pulse period between moments of maximum brightness, the greater the maximum brightness. The relationship of period to luminosity allows us to accurately calculate our distance from Earth; It is possible to measure the period of the pulsation to calculate the maximum brightness, and then based on how bright the Cepheid variable in the sky is to us, we can figure out how far away it would have to be to appear that bright.
However, it is not a completely foolproof method.
The Hubble Space Telescope can spot Cepheid variables in distant galaxies, but the more distant they are, the harder it is to distinguish from all the other stars clustered around them. As such, there was concern that unresolved stars adjacent to the Cepheid variables in these distant galaxies were adding to the apparent brightness values of the Cepheids, creating an invisible and systematic error in the measurements. Interstellar dust can also affect the brightness of Cepheid variables, dimming them from our view on Earth.
But new measurements made with the James Webb Space Telescope of five galaxies hosting more than a thousand Cepheid variables have ruled out this possible error. JWST's infrared vision is able to penetrate interstellar dust, while its greater resolution allows it to resolve Cepheid variables so clearly that it stands out from the crowd. Through these James Webb Space Telescope measurements, astronomers led by Adam Ries of Johns Hopkins University determined that Hubble's original measurements were correct.
“We have now covered the full range of what Hubble observed, and we can rule out measurement error as a cause of Hubble jitter with very high confidence,” Rees said in his research. statement.
The five galaxies observed by the James Webb Space Telescope, the most distant of which is NGC 5468 at 130 million light-years from us, have also hosted a total of eight Type Ia supernovae over recent decades. These supernovae, which indicate destruction White dwarfs, has a measurable luminosity curve, and constitutes the next rung on the cosmic distance scale above Cepheids. Because the previous degree is required to calibrate the next degree, the James Webb Space Telescope's observations of Cepheid variables make distance measurements using Type Ia supernovae – which are bright enough to be seen in galaxies much farther away than Cepheid galaxies – more accurate. They also tell us that there is a discrepancy in different measurements of the Hubble constant.
“With measurement errors negated, what remains is the real and exciting possibility that we have misunderstood the universe,” Rees said.
The team's results are a long time coming, as they have been available On the arxiv preprint server Gaining chatter late last year. But now that it's been fully published, perhaps we can finally close the chapter on blaming Hubble's stress on Hubble itself.
Reiss's team's results were published on February 6 in Astrophysical Journal Letters.
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