Now, the state of the art has been further developed with both Hubble and Webb working together to provide a broad-spectrum view of thousands of young star clusters. An international team of astronomers has pored over images of four nearby galaxies – Messier 51, Messier 83, NGC 4449, and NGC 628 – from the FEAST observing programme (#1783), trying to solve this mystery. Their results, published today in Nature Astronomy, show that it is the most massive star clusters that clear away their gaseous shroud the fastest, and begin lighting their galaxy the earliest.

The team identified nearly 9000 star clusters in the four galaxies in different evolutionary stages: young clusters just starting to emerge from their natal clouds of gas, clusters that had partially dispersed the gas (both from Webb images), and fully unobstructed clusters visible in optical light (found in Hubble images). With Webb’s ability to peer inside the gas clouds, they were able to then estimate the mass and age of each cluster from its light spectrum. The most massive clusters had fully emerged and dispersed the clouds of gas after around five million years, while less massive clusters were between seven and eight million years old when they emerged from their nurseries.

Answering this open question of which star clusters clear away their birth clouds the fastest advances our understanding of galaxy formation. “Simulations of star formation and stellar feedback have struggled to reproduce how star clusters form and emerge from their natal clouds. These results give us important new constraints on that process,” explained Angela Adamo of Stockholm University and the Oskar Klein Centre in Sweden, a lead author on the study and PI of the FEAST programme.