The influence of magnetic fields on second-generation star formation in globular clusters

ABSTRACT We investigate the previously unexplored role of magnetic fields in the formation of second-generation (SG) stars in proto-globular clusters (GCs) using 3D radiation-magnetohydrodynamical simulations. This study is based on the asymptotic giant branch (AGB) scenario and incorporates photoionization feedback and stellar winds from AGB stars. We model SG formation within a young ($34\, \mathrm{Myr}$) massive ($10^6\, \mathrm{M}_{\odot }$) proto-GC moving through a magnetized, homogeneous interstellar medium. Our results indicate that variations in magnetic field strength and orientation significantly influence the gas geometry and SG star-forming regions around the cluster. Overall, magnetic fields limit SG formation to the very centre of the cluster, with stronger magnetic fields tending to form more compact SG clusters. For magnetic field strengths of 0.5 and $5\, \mathrm{\mu \, G}$, we observe no substantial changes in the mass of formed SG stars. However, with a strong $50\, \mathrm{\mu \, G}$ field, we see a 25 per cent increase or a 70 per cent decrease in total SG mass, for a field aligned parallel or perpendicular to the cluster’s motion, respectively. This variation reflects how magnetic fields influence gas accretion, as our results suggest that gas accreted from the interstellar medium (ISM) slightly dominates over AGB ejecta in the cluster—except in cases of strong perpendicular fields, where gas accretion is efficiently suppressed. Additionally, stronger magnetic fields limit the cluster’s ability to retain its ejecta, leading to the formation of stars with lower helium abundances. On the other hand, a strong perpendicular magnetic field produces SG stars that originate from AGB ejecta and exhibit the highest helium abundances.