Issue |
A&A
Volume 699, July 2025
|
|
---|---|---|
Article Number | A223 | |
Number of page(s) | 15 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361/202453462 | |
Published online | 09 July 2025 |
Collision-induced mass loss and mass gain on an extremely massive star
An analytical approach and a static proto-globular cluster test-case
1
Department of Astronomy, University of Geneva, Chemin Pégasi 51, 1290 Versoix, Switzerland
2
IRAP, UMR 5277 CNRS and Université de Toulouse, 14 Av. E. Belin, 31400 Toulouse, France
3
Gravitational Wave Science Center (GWSC), Université de Genève, 24 quai E. Ansermet, CH-1211 Geneva, Switzerland
4
CMAP, CNRS, École Polytechnique, Institut Polytechnique de Paris, 91120 Palaiseau, France
5
ICREA, Pg. Lluís Companys 23, E08010 Barcelona, Spain
6
Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Martí i Franquès 1, E08028 Barcelona, Spain
⋆ Corresponding author: laura.ramirezgaleano@unige.ch
Received:
16
December
2024
Accepted:
28
May
2025
Aims. The objective of this study is to analytically explore mass loss and gain induced by stellar collisions on a gas-accreting extremely massive star (aEMS, 103≲M/M⊙≲104). We also consider its contribution to the mass budget in the context of forming multiple stellar populations (MPs) in a typical protoglobular cluster (GC).
Methods. We used MESA to build a series of aEMS models up to 2×104 M⊙ for three [Fe/H] values, covering the metallicity range of Galactic GCs, with different treatments of super-adiabatic convection. We set analytical prescriptions to quantify collision-induced mass loss when a star spirals and deposits energy into the envelope of the aEMS. We used a Monte Carlo approach to simulate the effects of multiple collisions on an aEMS of initial mass of 103 M⊙ in a static proto-GC, accounting for mass loss and gain from collisions, gas accretion, and stellar winds.
Results. We show that assumptions on super-adiabaticity in radiation-dominated layers significantly impact the aEMSs properties and their collision responses: extended stars tend to lose mass, while compact ones are more likely to gain it. Our MC simulations predict the total mass lost and gained, along with the corresponding timescales and contributions from stellar winds and collisions. The results are influenced by the structural characteristics of the aEMS and by the gas accretion rate during the collision phase. Under certain conditions, the EMS exhibits a “conveyor belt” behavior, processing up to 105.5 M⊙ of material in ∼5 Myrs.
Conclusions. This study provides theoretical predictions supporting aEMSs as contributors to the abundance anomalies observed in GCs. It emphasizes the importance of including collision dynamics and mass transfer in aEMS formation and evolution models in dense stellar environments. We provide a grid of predictions for stellar M-R-[Fe/H]-structure relations and collision-induced mass loss and gain, suitable for inclusion in hydro and N-body simulations of star clusters.
Key words: stars: abundances / stars: chemically peculiar / stars: mass-loss
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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