Kavli Affiliate: Rainer Spurzem
| First 5 Authors: Marcelo C. Vergara, Abbas Askar, Albrecht W. H. Kamlah, Rainer Spurzem, Francesco Flammini Dotti
| Summary:
Context. We present simulations of a massive young star cluster using
textsc{Nbody6++GPU} and textsc{MOCCA}. The cluster is initially more compact
than previously published models, with one million stars, a total mass of $5.86
times 10^5~mathrm{M}_{odot}$, and a half-mass radius of $0.1~mathrm{pc}$.
Aims. We analyse the formation and growth of a very massive star (VMS)
through successive stellar collisions and investigate the subsequent formation
of an intermediate-mass black hole (IMBH) in the core of a dense star cluster.
Methods. We use both direct textit{N}-body and Monte Carlo simulations,
incorporating updated stellar evolution prescriptions (SSE/BSE) tailored to
massive stars and VMSs. These include revised treatments of stellar radii,
rejuvenation, and mass loss during collisions. While the prescriptions
represent reasonable extrapolations into the VMS regime, the internal structure
and thermal state of VMSs formed through stellar collisions remain uncertain,
and future work may require further refinement.
Results. We find that runaway stellar collisions in the cluster core produce
a VMS exceeding $5 times 10^4~mathrm{M}_{odot}$ within 5 Myr, which
subsequently collapses into an IMBH.
Conclusions. Our model suggests that dense stellar environments may enable
the formation of very massive stars and massive black hole seeds through
runaway stellar collisions. These results provide a potential pathway for early
black hole growth in star clusters and offer theoretical context for
interpreting recent JWST observations of young, compact clusters at high
redshift.
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