An international team led by ICREA researcher Mark Gieles, from the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Institute of Space Studies of Catalonia (IEEC), has developed a groundbreaking model that reveals how extremely massive stars (EMS) - with more than 1,000 times the mass of the Sun - have governed the birth and early evolution of the oldest star clusters in the universe.
The study, published in the journal Monthly Notices of the Royal Astronomical Society, reveals how these short-lived stellar giants profoundly influenced the chemistry of globular clusters (GCs), which are some of the oldest and most enigmatic star systems in the cosmos.
Globular clusters: the ancient archives of the universe
Globular clusters are dense, spherical groups of hundreds of thousands or millions of stars found in almost all galaxies, including the Milky Way. Most are more than 10 billion years old, indicating that they formed shortly after the Big Bang.
Their stars display puzzling chemical signatures, such as unusual abundances of elements like helium, nitrogen, oxygen, sodium, magnesium, and aluminium, which have defied explanation for decades. These "multiple populations" point to complex enrichment processes during cluster formation from extremely hot "contaminants".
A new model for cluster formation
The new study is based on a star formation model known as the inertial-inflow model, extending it to the extreme environments of the early universe. The researchers show that, in the most massive clusters, turbulent gas naturally gives rise to extremely massive stars (EMS) weighing between 1,000 and 10,000 solar masses. These EMSs release powerful stellar winds rich in high-temperature hydrogen combustion products, which then mix with the surrounding pristine gas and form chemically distinct stars.
