An international team of astronomers has used the James Webb Space Telescope to solve a long-standing puzzle about why some distant galaxies abruptly ceased forming stars. The study, published in the Monthly Notices of the Royal Astronomical Society, examined a large sample of recently “quenched” galaxies observed as they appeared roughly nine billion years ago.
The findings, led by researchers at the University of Nottingham, reveal that these galaxies bear unmistakable “merger scars” — evidence of violent collisions with other galaxies. Such mergers are thought to have disrupted the gas reservoirs needed for star formation, effectively shutting down the galactic nurseries.
Webb’s infrared sensitivity allowed the team to peer through cosmic dust and identify the structural distortions unique to recent mergers. The data provide the clearest link yet between galaxy collisions and the sudden halting of star formation in the early universe.
The results challenge the notion that internal processes alone drive quenching. Instead, they point to external cosmic events as a primary mechanism, reshaping our understanding of galactic life cycles.
While compelling, the study is limited by the small sample size relative to the total population of quenched galaxies, and future surveys will need to confirm whether merger scars are indeed universal among such systems.