Light element variations in globular clusters via nucleosynthesis in black hole accretion discs

Ancient globular clusters contain multiple stellar populations identified by variations in light elements (e.g. C, N, O, Na). Although many scenarios have been suggested to explain this phenomenon, all are faced with challenges when compared with all the observational evidence. In this Letter, we propose a new scenario in which light element variations originate from nucleosynthesis in accretion discs around black holes. Since the black holes form after a few Myrs, the cluster is expected to still be embedded in a gas-rich environment. Through a simplified accretion model, we show that the correct light element anticorrelations can be produced. Assuming a Kroupa stellar initial mass function, each black hole would only have to process ≈300 M⊙ of material in order to explain multiple populations; over a period of 3 Myr this corresponds to ∼10−4 M⊙ yr−1 (similar to the estimated accretion rate for the X-ray binary SS 433).