Ballistic mixing: Stellar mergers drive internal mixing in extremely massive stars with implications for proto-globular cluster pollution

Extremely massive stars, with masses of 10^3--10^4 have been proposed as potential sources of the chemical enrichment associated with multiple populations in globular clusters. Early in the main sequence, these stars reach central temperatures of 65 to 75 MK, enabling nucleosynthesis through the CNO, NeNa, and MgAl cycles and producing abundance patterns similar to those observed in the so-called cluster's second population. Among the leading formation channels for extremely massive stars are stellar mergers. We followed the formation of a sim6700 star via 253 stellar mergers drawn from a direct N-body star cluster simulation with properties similar to the densest star clusters observed at redshift z We evolved each star as a 1D stellar model and constructed the merger products from mixing and shock-heating prescriptions calibrated to 3D simulations of parabolic collisions. We find that entropy-based mixing efficiently transports nuclear-processed material from the convective core to the envelope, while merger-driven heating promotes chemical homogenization. As a result, the stellar surface becomes enriched with H-burning products, producing abundance patterns consistent with those observed in multiple stellar populations in globular clusters and supporting the role of extremely massive stars formed through mergers as potential sources of early chemical enrichment in proto-globular cluster-like conditions.