Efficient black hole seed formation in low-metallicity and dense stellar clusters with implications for JWST sources
Year: 2026
Type: article
Abstract: Context . Recent observations with the James Webb Space Telescope (JWST) have revealed the presence of young massive clusters (YMCs) as building blocks of the first galaxies during the first billion years of the Universe. They are not only important constituents of the galaxies, but also potential birthplaces of very massive stars (VMSs) and black hole (BH) seeds. Aims . In this paper, we investigate whether runaway stellar collisions in extremely dense clusters inevitably lead to the formation of VMSs and BH seeds. We focus on clusters with initial half-mass densities of ρ h ≳ 10 8 M ⊙ pc −3 at very low metallicity ( Z = 10 −4 ), using idealized initial conditions that assume a fully formed, gas-free, monolithic stellar system. Our goal is to follow their early internal evolution and quantify the efficiency of collisional growth. Methods . We use NBODY 6++ GPU and MOCCA, including the latest updates of the single stellar evolution (SSE) and binary stellar evolution (BSE), along with specific routines to handle the formation, growth through collisions, and dynamical evolution of VMSs. Results . Our direct N -body and Monte Carlo simulations show that VMSs form rapidly and unavoidably through repeated collisions, reaching final masses of ~5 × 10 3 to 4 × 10 4 M ⊙ , before collapsing into BH seeds of similar mass in less than 4 Myr. These results confirm the existence of a critical mass scale at which collisional growth becomes highly efficient, enabling the formation of VMSs and potentially intermediate-mass BHs. Conclusions . We identify a critical mass–density threshold beyond which clusters undergo runaway collisions, leading to efficient BH-seed formation. For YMCs detected with JWST, we expect efficiencies up to ~10%, corresponding to BH masses as large as 10 5 M ⊙ . We predict a BH mass–cluster mass scaling relation of log( M BH / M ⊙ ) = −0.76 + 0.76 log(M / M ⊙ ). Frequent VMS formation in this regime may also provide a natural explanation for the strong nitrogen enrichment observed in some high-redshift galaxies.
Source: Astronomy and Astrophysics
Institutions: Heidelberg University, Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, New York University Abu Dhabi, Sapienza University of Rome, University of Concepción, University of Chile, Chinese Academy of Sciences, Peking University, National Astronomical Observatories, ARC Centre of Excellence for Gravitational Wave Discovery, University of Padua, Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Gran Sasso, Collurania Teramo Observatory, Gran Sasso Science Institute, National Institute for Astrophysics, Max Planck Institute for Astronomy
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: National Science Foundation, New York University Abu Dhabi, International Max Planck Research School for Environmental, Cellular and Molecular Microbiology, European Commission, Deutscher Akademischer Austauschdienst, Deutsche Forschungsgemeinschaft, Universität Heidelberg, National Natural Science Foundation of China, Centro de Astrofísica y Tecnologías Afines, International Max Planck Research School for Advanced Methods in Process and Systems Engineering, Fondation Merac, Tamkeen, Agencia Nacional de Investigación y Desarrollo, Gauss Centre for Supercomputing, National Astronomical Observatories, Chinese Academy of Sciences, Kavli Institute for Theoretical Physics, University of California, Santa Barbara
Awards: Postdoctoral Fellowships in Poland to Boost International Mobility and Skills Training, G1750626284, G1820675529, G2329447088, G3183642665, G3398237449, G434337789, G4689434848, G5109189900, Gravitational waves from crowded environments: simulating intermediate-mass black hole formation and evolution with supercomputers., G5834573078, G5857371469, G595377943, Kavli Institute for Theoretical Physics, THE NEXT STEP FOR ASTROPHYSICAL SUPERCOMPUTING IN CHILE A POWERFUL GPU-SERVER FOR FLUID AND STELLAR DYNAMICS, G8382749824, CENTRO DE ASTROFISICA Y TECNOLOGIAS AFINES (CATA)
OpenAlex ID: W4415238766