The James Webb Space Telescope (JWST) has provided measurements of the Universe's expansion rate, known as the Hubble Constant (H0), and the results align with those from the Hubble Space Telescope. This finding suggests that the Hubble data is not flawed, leaving the long-standing cosmological mystery of the "Hubble tension" unresolved.
The Hubble Constant represents the rate at which the Universe expands, and different measurement methods have yielded conflicting results. One approach involves studying remnants of the early Universe, like the cosmic microwave background or frozen acoustic waves. The other method measures distances to objects with known intrinsic brightness, such as Type Ia supernovae or Cepheid variable stars.
The first method suggests an expansion rate of around 67 kilometres per second per megaparsec, while the second indicates approximately 73 kilometres per second per megaparsec. This disparity between measurements is the Hubble tension.
To address this tension, scientists have employed both methods repeatedly to reduce the likelihood of errors. However, some Cepheid variable data, crucial for H0 measurements, comes primarily from the Hubble Space Telescope.
The problem lies in the crowded nature of stars in galaxies, making distinguishing individual Cepheid variables from their line-of-sight neighbours challenging. Hubble was designed to resolve this issue by operating above Earth's blurring atmosphere, but it was less effective in the near-infrared part of the spectrum.
The JWST, a powerful infrared telescope, was used to observe Cepheids in galaxies, overcoming the limitations faced by Hubble. JWST's observations of 320 Cepheids matched the distances determined using Hubble data, indicating that calculations of H0 based on Hubble data, at 73 kilometres per second per megaparsec, remain valid.
This means that human error is unlikely to cause the Hubble tension. The mystery behind the disagreement between the two measurement methods remains, with one leading hypothesis suggesting dark energy, an enigmatic force accelerating the Universe's expansion.
While JWST's measurements reinforce the credibility of Hubble's data, the deeper question regarding the source of the Hubble tension remains unanswered. The tension persists, and dark energy remains a key candidate for explaining this cosmological conundrum.