The deaths of massive stars formed the earliest star clusters, scientists have discovered in a new study published in the journal Monthly Notices of the Royal Astronomical Society. A study has revealed that the turbulent gas in ancient star clusters enabled the formation of very large stars, approximately 10,000 times larger than our Sun. These massive stars dispersed the enriched winds from high-temperature hydrogen fusion throughout the gas remaining in clusters, giving rise to new generations of chemically distinct stars. This process accounts for the special chemical signatures in globular clusters, such as their enrichment in helium, nitrogen, oxygen, sodium, magnesium, and aluminum—a puzzle that had left astronomers scratching their heads for decades.
According to the Large Survey of 198 BStars team, led by Laura Ramirez Galeano and Corinne Charbonnel at the University of Geneva, only a few of these massive stars left their mark on entire clusters. These stars enriched their environments on timescales of ≈1−2 Myr after the birth of the clusters, well in advance of any pollution by supernovae. The study also notes that these heavy stars likely ended their lives as intermediate-sized black holes, possibly up to 200 times the mass of the Sun, which could be observable through gravitational waves.
This new framework integrates the physics of star formation, cluster expansion, and chemical enrichment to demonstrate that supermassive stars were responsible for creating the first galaxies and their accompanying star clusters. The study also presents an interesting opportunity to understand the very distant protogalaxies observed by JWST, where so-called nitrogen-rich galaxies could be harbouring star clusters dominated by such massive stars. Paolo Padoan of Dartmouth College emphasized their importance in accounting for the high luminosity and nitrogen enhancement observed in early galaxies.
Globular star clusters themselves are old, highly dense groups of tens of thousands to a few million stars, all packed into regions ranging from 50 to 450 light-years across. They exist in galaxies, including our own Milky Way. Still, some 150 or so such clusters circle the halo of our galaxy, orbiting in retrograde orbits, which indicates they were captured from other galaxies during engagements. These clusters coalesced between approximately 8 to 13 billion years ago and contain some of the universe’s earliest stars — stellar fossils from which astronomers can glean critical information about when galaxies began to form and evolve.
The discovery sheds light on the early history of stars and galaxies, offering clues about the chemical elements essential for life, as well as the formation of behemoths — the first black holes. The research synthesizes theory, observation, and recent data from state-of-the-art instruments — such as the JWST — making a significant leap in understanding how the cosmos took shape during some of its earliest years.
This study alters our understanding of the influence of massive stars on the formation of the universe’s oldest star clusters, thereby shedding light on the origins of chemical complexity, galactic structure, and stellar evolution in the early cosmos.