Where do giant black holes come from? Webb may have found their birthplaces

The biggest black holes in the universe had to start somewhere — and the James Webb Space Telescope may have caught their seeds at home. A team led by Viola Bocchi of Sapienza University of Rome studied young, dense star clusters in two galaxies seen as they were less than 600 million years after the Big Bang: five clusters in the Cosmic Gems arc and ten in the Firefly Sparkle galaxy. Their modelling, published in Astronomy & Astrophysics, points to middleweight black holes of roughly 100 to 4,000 times the Sun's mass forming inside those clusters — heavy seeds that could grow, over cosmic time, into the giants at galaxy centres. The clusters' sparse chemistry seems to help: with few heavy elements, the growing seeds keep more of their mass.