Ballistic mixing: stellar mergers drive internal mixing in extremely massive stars, with implications for proto-globular cluster pollution
Abstract
Extremely massive stars, with masses of 103-104 M⊙, have been proposed as potential sources of the chemical enrichment associated with multiple populations in globular clusters. Early on the main sequence, these stars reach central temperatures of 65 to 75 MK, enabling nucleosynthesis through the CNO, NeNa, and MgAl cycles, producing abundance patterns similar to those observed in the so-called cluster's second population. Stellar mergers are among the leading formation channels for extremely massive stars. In this work, we follow the formation of a ∼6700 M⊙ 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∼10. We evolve each star as a 1D stellar model and construct 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 globular cluster multiple populations and supporting the role of merger-formed extremely massive stars as potential sources of early chemical enrichment in proto-globular cluster-like conditions.
Related
- A Theoretical Study of the Stellar Parameters and Surface Nucleosynthesis of the Extremely Metal-Poor RGB Giant BD−18∘5550 - Part I: Effects of α-enhancement and Internal Mixing
- Stable Ballistic Prograde Cyclers in the Three-Body Problem
- Playing CHESS with stars. II. Homogeneous analysis of high-resolution optical spectra for a sample of 135 giants in 14 bulge globular clusters
- Globular cluster Observations for Luminosity-dispersion Distances (GOLD): Project description and velocity catalogue
- Reconstructing the Globular Cluster Initial Mass Function from Present-day Globular Cluster Systems
BibTeX
@misc{romangarza2026ballistic,
title = {{Ballistic mixing: stellar mergers drive internal mixing in extremely massive stars, with implications for proto-globular cluster pollution}},
author = {J. Roman-Garza and C. Charbonnel and A. Rantala and T. Fragos and M. Gieles and L. Ramírez-Galeano},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.29369},
eprint = {2610.29369},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.29369},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Ballistic mixing: stellar mergers drive internal mixing in extremely massive stars, with implications for proto-globular cluster pollution
AU - J. Roman-Garza
AU - C. Charbonnel
AU - A. Rantala
AU - T. Fragos
AU - M. Gieles
AU - L. Ramírez-Galeano
PY - 2026
DA - 2026/10/21
PB - arXiv
DO - 10.48550/arxiv.2610.29369
UR - https://arxiv.org/abs/2610.29369
AB - Extremely massive stars, with masses of 10^3-10^4 M_⊙, have been proposed as potential sources of the chemical enrichment associated with multiple populations in globular clusters. Early on the main sequence, these stars reach central temperatures of 65 to 75 MK, enabling nucleosynthesis through the CNO, NeNa, and MgAl cycles, producing abundance patterns similar to those observed in the so-called cluster's second population. Stellar mergers are among the leading formation channels for extremely massive stars. In this work, we follow the formation of a ∼6700 M_⊙ 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∼10. We evolve each star as a 1D stellar model and construct 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 globular cluster multiple populations and supporting the role of merger-formed extremely massive stars as potential sources of early chemical enrichment in proto-globular cluster-like conditions.
ER -