Webb confirms the validity of the universe’s expansion rate and deepens the mystery of Hubble’s constant tension

The rate at which the universe is expanding, known as the Hubble constant, is one of the fundamental parameters for understanding the evolution and ultimate fate of the universe. However, there is a persistent difference called the “Hubble voltage” observed between the value of the constant measured by a series of independent distance indicators and its value predicted from the remnant of the Big Bang.

NASA’s James Webb Space Telescope provides new capabilities to test and refine some of the strongest observational evidence for this tension. Adam Riess, a Nobel laureate from Johns Hopkins University and the Space Telescope Science Institute, presents his and his colleagues’ recent work using Webb observations to improve the precision of measurements locality of the Hubble constant: .. located at the edge of your vision? What does it say?What does it mean? Even with the most powerful telescopes, the “signs” astronomers want to read seem so small that we struggle. number is called the Hubble constant. Our sign is written on the stars of distant galaxies. The brightness of certain stars in these galaxies tells us how far away they are and therefore how long it took that light to reach us, and the redshift of the galaxies tells us how much the universe has expanded over time. expansion speed.”

“A particular type of star, the Cepheid variable star, has provided us with our most precise distance measurements for more than a century because these stars are extremely bright: they are supergiants, with hundreds of thousands of times brighter than the sun. (i.e. expansion and contraction) over a period of several weeks indicates their relative brightness. The longer the time period, the brighter they are in nature.

” They are the reference instrument for measuring the distances of galaxies located one hundred million light-years or more away, an important step in determining the Hubble constant. Unfortunately, the stars of these galaxies are compressed into a tiny space on our planet’s distant viewpoint, and so we often lack solutions to separate them from their visible neighbors.” ” One of the main reasons for building the Hubble Space Telescope was to solve this problem. Before Hubble’s launch in 1990 and subsequent measurements of the Cepheids, the rate of expansion of the universe was so uncertain that astronomers did not know whether the universe had been expanding for 10 or 20 billion years. . This is because a faster rate of expansion would lead to a younger age of the universe, and a slower rate of expansion would lead to an older age of the universe. »

“Hubble has better visible wavelength resolution than any ground-based telescope because it is superior to the blurring effect of Earth’s atmosphere. As a result, it can identify variations Individual Cepheids in galaxies lie more than a hundred million light years distant and measure the time period during which they change brightness.”

“However, we also need to observe Cepheids in the near-infrared part of the spectrum to see light pass through the intervening dust layer without damage. (Dust absorbs and scatters blue optical light blue, making distant objects appear pale and causing us to believe they are farther away than they actually are.”

“Unfortunately, Hubble’s vision of red light is not sharp like blue light, so the light from the Cepheid stars we see there is mixed with other stars in its field of view.We can calculate the average mixture statistically, the same way a doctor calculates your weight by subtracting the average weight of clothing from the scale reading, but this adds noise. for measurements. Some people’s clothes are heavier than others. »

“However, sharp infrared vision is one of the James Webb Space Telescope’s superpowers. With its large mirror and sensitive optics, it can readily separate the Cepheid light from neighboring stars with little blending. In the first year of Webb operations with our General Observers program 1685, we collected observations of Cepheids found by Hubble at two steps along what’s known as the cosmic distance ladder.”

“The first step involves observing Cepheids in a galaxy with a known, geometric distance that allows us to calibrate the true luminosity of Cepheids. For our program that galaxy is NGC 4258. The second step is to observe Cepheids in the host galaxies of recent Type Ia supernovae.”

“The combination of the first two steps transfers knowledge of the distance to the supernovae to calibrate their true luminosities. Step three is to observe those supernovae far away where the expansion of the universe is apparent and can be measured by comparing the distances inferred from their brightness and the redshifts of the supernova host galaxies. This sequence of steps is known as the distance ladder.”

“We recently got our first Webb measurements from steps one and two which allows us to complete the distance ladder and compare to the previous measurements with Hubble Webb’s measurements have dramatically cut the noise in the Cepheid measurements due to the observatory’s resolution at near-infrared wavelengths.”

“This kind of improvement is the stuff astronomers dream of! We observed more than 320 Cepheids across the first two steps. We confirmed that the earlier Hubble Space Telescope measurements were accurate, albeit noisier. We have also observed four more supernova hosts with Webb and we see a similar result for the whole sample.”

“What the results still don’t explain is why the universe appears to be expanding so rapidly! We can predict the expansion rate of the universe by observing its baby image, the cosmic microwave background, and then using our best model of its evolution.” it’s time to tell us how fast the universe is expected to expand today.”

“Measuring current expansion rates that far exceed predictions is a decades-long problem known as is the ‘Hubble Tension’. The most exciting possibility is that tension is a clue to something we are missing in our understanding. of the universe.”

“This could indicate the presence of exotic dark energy, exotic dark matter, a change in our understanding of gravity or the presence of a single county or field.The most mundane explanation might be that multiple measurement errors are all in the same direction (astronomers rule out a single error by using independent steps), which is why re-measuring with Greater precision is so important. ” ” With Webb confirming Hubble’s measurements, Webb’s measurements provide the strongest evidence to date that systematic errors in Hubble’s Cepheid photometry did not play a significant role in the variation. Hubble’s current form. As a result, the most exciting possibilities remain on the table and the mystery of the tension deepens.”

This post highlights data from a paper that was accepted by The Astrophysical Journal.