James Webb reveals a galaxy that challenges theory

The James Webb Space Telescope, operational since 2022, was specifically designed to observe the early universe with unprecedented precision. Its infrared instruments allow detection of the light from galaxies that formed just hundreds of millions of years after the Big Bang, redshifted by the expansion of the universe during the 13 billion years it took to reach us. The first years of operation produced discoveries that no one expected to find so soon.

The galaxy JADES-GS-z14-0, identified in 2024, has a redshift of 14.32, meaning we are seeing it as it was when the universe was just 290 million years old. For that period, standard cosmological models predicted small, low-mass galaxies with low stellar production. JADES-GS-z14-0 shows exactly the opposite: it is brighter, larger and has a significantly higher star formation rate than the models allowed. Its estimated stellar mass is several hundred million solar masses — a figure cosmologists considered impossible for that era of the universe.

The finding does not refute the standard cosmological model — the Big Bang and the expansion of the universe are not in question — but it does indicate that galaxy formation processes in the early universe were significantly faster than current models reproduce. Cosmologists are working on alternative hypotheses: greater efficiency of dark matter in structure formation, stellar feedback mechanisms different from those modelled, or stellar populations with characteristics different from the stars we know. The Webb will continue accumulating data that will help choose between those hypotheses.