The James Webb Space Telescope has uncovered a surprising population of massive galaxies in the early universe that had already ceased star formation — a process astronomers call quenching — hundreds of millions of years earlier than previously thought.
By analyzing the morphology of these galaxies, researchers found that mergers between galaxies, which were hidden from earlier telescopes, are the driving mechanism behind this premature shutdown. The JWST's ability to observe highly red-shifted light was key to revealing these interactions.
The findings challenge existing models of galaxy evolution, which predicted that such massive quenched galaxies would not appear so early in cosmic history. The new data suggests that galaxy mergers play a more dominant role in quenching than previously accounted for.
This discovery marks a significant step in understanding how galaxies evolve and die, offering a glimpse into the early universe's dynamic processes. However, the sample size remains limited, and further observations are needed to confirm whether these mergers are indeed the primary cause across all early massive galaxies.
Counter to the merger hypothesis, some astronomers argue that feedback from supermassive black holes or intense star formation bursts could also quench galaxies without visible mergers, and that the JWST's view may still miss other quenching mechanisms.