Schematic view of GC formation. Turbulence is driven primarily by SNe on a scale of ~100 pc, leading to inertial flows on that scale. In the centre, a cluster of stars accumulates, together with a reservoir of gas that did not make it onto stars. After some time, the most massive stars have reached the Extremely Massive Star (EMS) regime (≳103 M⊙) and the pristine gas of the gas reservoir mixes with EMS winds that contain hot-hydrogen burning products. Low-mass stars (≲1 M⊙) continuously form from this mixture, which in approximately the second half of the GC formation process has approximately the abundances found in GCs.

Relation between abundance variations and central temperature, Tc, for different moments in the evolution quantified by ∆Ynorej from the nucleosynthesis results of Prantzos et al. (2017). The top axes show corresponding stellar masses, m, for different ∆Y. All stars ≳10 M⊙ are able to give rise to the O-Na anticorrelation, and masses ≳3×103 M⊙ are needed to get a significant Mg depletion and Al increase.