Is the James Webb Space Telescope rewriting the history of the early universe?

Space · Published 7 October 2026 Swipe more like this →

In short: The James Webb Space Telescope is uncovering a cosmos far more crowded and complex than our models predicted. From unexpectedly massive early galaxies to a deepening crisis in how we measure the universe's expansion, this powerful instrument is challenging the very foundations of modern cosmology.

Since coming online in mid-2022, the James Webb Space Telescope (JWST) has begun sweeping away long-held preconceptions about the early universe. One of its most striking revelations involves the mass of early galaxies. Astronomers previously assumed that these young cosmic structures were less massive, but JWST has revealed a hidden population of faint, small stars tucked between the brightest, most massive stars. By combining JWST data with observations from the Very Large Telescope (VLT), researchers studied nine early galaxies that had finished their intense star-formation periods. They discovered that the proportion of these small stars is much higher than in modern galaxies like the Milky Way, suggesting these early 'cosmic cities' are significantly more massive than previous estimates suggested.

The telescope has also uncovered 'universe breaker' galaxies that have sent shockwaves through the scientific community. Formed only 500 million years post-Big Bang, these six massive galaxies seem to hold a stellar count comparable to our Milky Way. This discovery has sparked debate: while some suggest these galaxies are truly massive, others propose they might simply be glowing with unusual brightness. Either way, they challenge our current understanding of how galaxies first bloomed.

Beyond galaxy evolution, the JWST is intensifying the 'Hubble tension'—a crisis in cosmology regarding the universe's expansion rate. The Planck satellite indicates an expansion of 67 km/s/Mpc, whereas Hubble previously estimated 73 km/s/Mpc, but JWST recorded 74 km/s/Mpc. This discrepancy suggests that the standard model of cosmology may be incomplete, potentially requiring new physics to resolve the disagreement.

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