Formation of Heavy Seed Black Holes and Little Red Dots-like Compact Clusters in Metal-enriched Star-forming Regions
Abstract
The origin of supermassive black holes (SMBHs) in the early Universe remains uncertain. While the classical direct-collapse scenario requires pristine gas exposed to intense Lyman-Werner (LW) radiation, recent JWST observations suggest that early growing BHs may reside in compact, metal-enriched environments. We investigate early BH formation using a cosmological radiation-hydrodynamic simulation that self-consistently follows the formation and evolution of rapidly accreting supermassive stars (SMSs). We find that intense LW radiation develops in clustered star-forming regions; by the time the first heavy seed forms, the mass-weighted internal intensity has reached J21∼1000. Most seeds form in weakly metal-enriched gas with [Z/H]∼−3 to −2, because the strongest LW fields occur in regions already enriched by previous stellar feedback. All halos above 109M⊙ in our zoom-in region host a BH more massive than 105M⊙. We construct stellar spectra using MIST/PHOENIX libraries for normal stars and 6000 K blackbody spectra for bloated SMSs. Five of eight massive clusters with stellar masses larger than 106 M⊙ exhibit intrinsically V-shaped spectra similar to those of Little Red Dots (LRDs). In the most prominent cases, luminous SMSs dominate the red optical emission, although Balmer breaks in normal stellar populations also contribute. We also identify off-center LRD-like systems in our simulation resembling those recently reported in strongly lensed observations. Our results suggest that heavy-seed formation, compact-cluster formation, and LRD-like continuum emission are linked outcomes of clustered, weakly metal-enriched, strongly irradiated environments.
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BibTeX
@misc{chon2026formation,
title = {{Formation of Heavy Seed Black Holes and Little Red Dots-like Compact Clusters in Metal-enriched Star-forming Regions}},
author = {Sunmyon Chon and Shingo Hirano and Ke-Jung Chen and Volker Springel},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.00437},
eprint = {2609.00437},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.00437},
}
RIS
TY - UNPB
TI - Formation of Heavy Seed Black Holes and Little Red Dots-like Compact Clusters in Metal-enriched Star-forming Regions
AU - Sunmyon Chon
AU - Shingo Hirano
AU - Ke-Jung Chen
AU - Volker Springel
PY - 2026
DA - 2026/09/01
PB - arXiv
DO - 10.48550/arxiv.2609.00437
UR - https://arxiv.org/abs/2609.00437
AB - The origin of supermassive black holes (SMBHs) in the early Universe remains uncertain. While the classical direct-collapse scenario requires pristine gas exposed to intense Lyman-Werner (LW) radiation, recent JWST observations suggest that early growing BHs may reside in compact, metal-enriched environments. We investigate early BH formation using a cosmological radiation-hydrodynamic simulation that self-consistently follows the formation and evolution of rapidly accreting supermassive stars (SMSs). We find that intense LW radiation develops in clustered star-forming regions; by the time the first heavy seed forms, the mass-weighted internal intensity has reached J_21∼1000. Most seeds form in weakly metal-enriched gas with [Z/H]∼−3 to −2, because the strongest LW fields occur in regions already enriched by previous stellar feedback. All halos above 10^9M_⊙ in our zoom-in region host a BH more massive than 10^5M_⊙. We construct stellar spectra using MIST/PHOENIX libraries for normal stars and 6000 K blackbody spectra for bloated SMSs. Five of eight massive clusters with stellar masses larger than 10^6 M_⊙ exhibit intrinsically V-shaped spectra similar to those of Little Red Dots (LRDs). In the most prominent cases, luminous SMSs dominate the red optical emission, although Balmer breaks in normal stellar populations also contribute. We also identify off-center LRD-like systems in our simulation resembling those recently reported in strongly lensed observations. Our results suggest that heavy-seed formation, compact-cluster formation, and LRD-like continuum emission are linked outcomes of clustered, weakly metal-enriched, strongly irradiated environments.
ER -