Understanding the cosmos’ evolution relies on the Hubble constant, a fundamental parameter representing the Universe’s expansion rate. The Hubble Tension, a persistent difference between measured values and predictions from the Big Bang’s afterglow, has been a challenge. The James Webb Space Telescope’s confirmation now validates the Hubble Space Telescope’s measurements, resolving uncertainties and reinforcing our comprehension of the Universe’s intricate dynamics.
The NASA/ESA Hubble Space Telescope, conceived with the purpose of precisely determining the Universe’s expansion rate, addressed significant uncertainties prevalent before its launch in 1990. Ground-based telescopic observations had yielded wide-ranging estimates, placing the age of the Universe anywhere between 10 and 20 billion years. Over the past 34 years, Hubble’s meticulous measurements have narrowed this range to an accuracy of less than one percent, settling on an age value of 13.8 billion years. This achievement involved refining the ‘cosmic distance ladder’ through the precise measurement of Cepheid variable stars, marking key milestones in our understanding of cosmic timelines.
The discrepancy between the Hubble value and measurements suggesting a faster post-Big Bang expansion, as observed by the ESA Planck satellite, has puzzled cosmologists. The Planck satellite’s mapping of cosmic microwave background radiation provides insight into the Universe’s structure evolution. To address this dilemma, one could question the accuracy of Hubble’s observations. However, the James Webb Space Telescope’s infrared views of Cepheids aligned with Hubble’s optical-light data, confirming Hubble’s accuracy.
The persistent Hubble Tension, comparing the nearby Universe to early expansion, remains a challenging puzzle. It raises questions about the need for new physics or potential measurement errors between different methods determining the space expansion rate, hinting at complexities yet to be fully understood in the fabric of space.
Hubble and Webb have collaborated to provide definitive measurements, reinforcing the idea that factors beyond measurement errors influence the expansion rate of the Universe. Adam Riess, a Nobel laureate known for co-discovering dark energy, expressed the exciting possibility of a misunderstood universe once measurement errors were ruled out. In 2023, Webb’s initial observation affirmed Hubble’s accuracy in measuring the expanding Universe.
To address the Hubble Tension, scientists considered potential unseen errors, particularly the impact of stellar crowding on brightness measurements of distant stars.The SH0ES team, led by Riess, utilized Webb to gather additional crucial observations of Cepheid variable stars, aligning with and corroborating Hubble’s data. This comprehensive approach aims to unravel the complexities influencing our understanding of the Universe’s expansion.
Riess confidently stated, “We’ve now spanned the whole range of what Hubble observed, and we can rule out a measurement error as the cause of the Hubble Tension with very high confidence.” The initial Webb observations in 2023 successfully affirmed Hubble’s accuracy in establishing the reliability of the first rungs of the cosmic distance ladder. Astronomers employ various techniques, collectively known as the cosmic distance ladder, for measuring relative distances in the Universe, with each method relying on the previous step for calibration. Concerns about the second rung’s stability arise as some astronomers suggest potential inaccuracies in Cepheid measurements with increasing distance.
The challenge lies in carefully accounting for blending effects as past Hubble images of distant Cepheids appear more crowded and overlapping with neighboring stars. Webb’s sharper infrared vision overcomes these challenges, slicing through dust and naturally isolating Cepheids from neighboring stars, enhancing the certainty of measurements compared to visible light observations by Hubble.
Riess emphasized the synergy of Webb and Hubble, stating, “Combining Webb and Hubble gives us the best of both worlds. We find that the Hubble measurements remain reliable as we climb farther along the cosmic distance ladder.” The recent Webb observations include five host galaxies of eight Type Ia supernovae, housing a total of 1000 Cepheids, extending to NGC 5468, the farthest galaxy with well-measured Cepheids at 130 million light-years. Co-author Gagandeep Anand of the Space Telescope Science Institute in Baltimore, operating both Webb and Hubble for NASA, noted that these observations span the full range of Hubble’s measurements, reaching the end of the second rung of the cosmic distance ladder.
The confirmation of the Hubble Tension by both Hubble and Webb sets the stage for other observatories to contribute to unraveling this cosmic mystery. Upcoming missions, such as NASA’s Nancy Grace Roman Space Telescope and ESA’s Euclid, hold promise in shedding further light on the expanding Universe. The analogy of a distance ladder, anchored by Hubble and Webb on one side and the Big Bang’s afterglow observed by Planck on the other, highlights the need to directly observe the Universe’s changes over billions of years between these two points. Riess emphasized the ongoing quest to understand potential missing links in connecting the Universe’s beginning with the present day. These groundbreaking findings were published in the 6 February 2024 issue of The Astrophysical Journal Letters.
