TOKYO -- Imagine a sprawling cosmic metropolis where ancient galaxies cluster together like skyscrapers in New York City. These galactic cities harbor a mysterious phenomenon: their largest residents have mysteriously stopped growing, their star-forming factories shut down long ago. Now, thanks to NASA's James Webb Space Telescope (JWST), astronomers may have caught the culprit red-handed -- supermassive black holes acting as cosmic kill switches.

A new study published in the Monthly Notices of the Royal Astronomical Society: Letters has revealed compelling evidence of how these cosmic giants might influence galaxy evolution. By examining an ancient "protocluster" called Spiderweb -- essentially a galaxy cluster under construction some 11 billion light-years away -- researchers have witnessed black holes apparently shutting down star formation in their host galaxies.

Led by Associate Professor Rhythm Shimakawa from Waseda University in Japan, an international team used Webb's Near Infrared Camera to study 19 massive galaxies within this distant cosmic nursery. What makes this study particularly fascinating is its timing - the researchers are observing these galaxies during the universe's peak period of star formation, when cosmic construction was in full swing.