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Have you ever wondered how fast the universe is expanding? Scientists have been asking this same question for years. In fact, it’s one of the most fundamental parameters for understanding the evolution and ultimate fate of the cosmos. This rate of expansion is known as the “Hubble Constant”, and measuring it precisely is an incredibly difficult task.A problem with measuring the Hubble Constant has been discovered. This problem is known as “Hubble Tension” and it’s seen between the value of the constant measured with a wide range of independent distance indicators and its value predicted from the big bang afterglow.
For decades, astronomers have been trying to resolve this issue. Recently, a breakthrough has been made with NASA’s James Webb Space Telescope. The telescope provides new capabilities to scrutinize and refine some of the strongest observational evidence for this tension. Nobel Laureate Adam Riess from the Johns Hopkins University and the Space Telescope Science Institute has presented his and his colleagues’ recent work in using Webb observations to improve the precision of local measurements of the Hubble Constant.The Hubble Constant is incredibly important because it helps us to understand how fast the universe is expanding and what its ultimate fate will be. It also helps us to understand how galaxies have moved away from each other since they were formed in the early universe.
Using Webb telescope observations, scientists are able to study distant galaxies in greater detail than ever before. This allows them to measure their redshifts and brightnesses more accurately, providing more precise measurements of their distances and hence giving us better information about the Hubble Constant.Webb observatory data has also been used to measure how structures in space evolve over time, giving us more information about how galaxies have moved away from each other since they were formed in the early universe. This helps us to better understand dark matter and dark energy – two mysterious components of the universe that are believed to be responsible for its accelerated expansion.
Webb observations have also been used to measure Type Ia supernovae, which provide a precise tool for measuring distances in space. By using these measurements alongside other data from Webb observatory, astronomers can better understand how far away galaxies are and hence gain a better understanding of the Hubble Constant.
Cepheid variables are a particular class of stars that have been used to provide the most precise measurements of distance for over a century. These stars are bright, being 100,000 times the luminosity of our sun, and also pulsate over a period of weeks that indicates their relative luminosity, with longer periods indicating a higher degree of brightness. As such, they make ideal tools for measuring the distance of galaxies that are up to 100 million light years away, allowing us to determine the Hubble constant. Unfortunately, when observing star fields from a distant vantage point, it can be hard to separate individual stars from their close neighbors due to their close proximity in space.
The Hubble Space Telescope was a major justification for its building, particularly for solving the problem of the uncertain expansion rate of the universe. Before its launch in 1990 and the subsequent Cepheid measurements, it was unclear if the universe had been expanding for 10 billion or 20 billion years. This is because a faster expansion rate would mean a younger age for the universe, and a slower expansion rate would mean an older age. Hubble is capable of providing better visible-wavelength resolution than any ground-based telescope due to sitting above the blurring effects of Earth’s atmosphere. This means Hubble can individually identify Cepheid variables in galaxies that are more than a hundred million light-years away and measure their changing brightness over time. This has enabled astronomers to gain a much better understanding of the age, size, and shape of the universe.
The Cepheids, which are essential for measuring distances in the universe, can be observed through the near-infrared part of the spectrum in order to get an accurate reading. This is because dust absorbs and scatters blue optical light which can make distant objects appear faint and further away than they actually are. However, even though Hubble has a powerful red-light vision, it is not as sharp as its blue and the Cepheid starlight seen there can often be blended with other stars in the same field of view. To solve this problem, a statistical method is used to subtract the average amount of blending from the measurements. This method is similar to how a doctor calculates weight by subtracting clothes weight from the scale reading. While this does add noise to measurements, it is still an effective way to get accurate readings of Cepheid stars.
The James Webb Space Telescope is capable of incredible feats of infrared vision which it can use to separate Cepheid light from other stars. Through the General Observers program, 1685 observations of Cepheids were collected in the first year of the telescope’s operation. This data was used to calibrate the true luminosity of Cepheids by comparing them to galaxies with known, geometric distances such as NGC 4258. This data was then used to calibrate the true luminosities of Type Ia supernovae in distant galaxies. Finally, by comparing the redshifts of these supernova host galaxies with their inferred distances, the expansion of the universe could be measured, completing the distance ladder.
Recently got first Webb measurements from steps one and two, allowing us to complete the distance ladder and compare it to the previous measurements from the Hubble telescope. Webb’s measurements have drastically reduced the noise in Cepheid measurements due to its outstanding resolution at near-infrared wavelengths. This is what astronomers have been dreaming of! Observed more than 320 Cepheids across the first two steps and confirmed that the Hubble Space Telescope measurements were accurate, albeit noisier. In addition, we observed four more supernova hosts using Webb and found a similar result for the whole sample, showing that Webb is a powerful tool for making precise and accurate observations.
The Hubble Tension is a decade-long problem that has puzzled scientists, as the expansion rate of the universe today significantly exceeds what can be predicted by observing its cosmic microwave background and applying our best model of how it grows over time. This suggests that there is something more to the universe than we currently understand. What makes this issue even more fascinating is that the universe appears to be expanding faster than expected – a mystery that has yet to be solved. The most exciting possibility is that this tension holds the key to unlocking the secrets of the cosmos, and it could lead to some amazing new discoveries in understanding of the universe.
The Hubble Tension is an intriguing mystery within the scientific community that may be indicative of something groundbreaking or simply the result of multiple measurement errors conspiring together. Recently, the Webb telescope was used to help confirm the measurements from Hubble, ruling out the possibility of systematic errors in Hubble’s Cepheid photometry and deepening the mystery further. Depending on the outcome, this could indicate a revolution in our understanding of dark energy, matter, gravity, or even the possibility of a unique particle or field. Regardless of what is ultimately discovered, this mystery has high stakes for the future of astronomy and could potentially bring about a whole new understanding of universe.
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