Primordial Black Hole Seeds for Little Red Dots in f(R) Gravity
Abstract
The little red dots (LRDs) discovered by the James Webb Space Telescope host black holes of up to 109 M⊙ within the first billion years, posing a challenge to conventional seeding scenarios. We investigate whether such seeds can form in dense clusters of primordial black holes (PBHs), in which the central object grows by gravitational capture of the surrounding PBHs while accreting gas, within Hu-Sawicki f(R) gravity, where the scalar field acts on the matter surrounding the PBHs. For the adopted cluster configuration, our results show that accretion and mergers reinforce one another: for time-averaged Eddington ratios λEdd≳0.3, the seed consumes its cluster by z≃5.5-$7.3$ and subsequently grows into the LRD mass range. Calibrated on the observed black-hole mass function, the model reproduces the abundance of LRDs near the peak of their population without further adjustment, while it underpredicts the abundance at z≃7.5 and overpredicts it at z≃2. Our findings indicate that the earliest seeds may accrete about twice as efficiently as later ones, and that the finite cluster reservoir can imprint a lower edge on the mass function near the cluster mass. Within the adopted screening and halo-growth prescriptions, the scalar field enhances the abundance of active seeds by up to ∼ 13% at lower redshifts and by ∼ 7% at z ≃ 7.5 for the strongest model considered, modestly moving the high-redshift prediction towards the data at fixed normalization. Also, the remnant spins can further discriminate between feeding modes.
Related
- Overmassive No More: The Case for Little Red Dots Hosting Black Hole Seeds as Massive as Single Supermassive Stars
- Black Hole Seeds and Little Red Dots: Connecting Formation and Growth with a JWST Multi-Cycle Treasury Program
- Small-Scale Clustering of Primordial Black Holes: The Little Red Dot Mass Function and the High-Redshift Galaxy Tension
- Heavy Seeds and the Multi-scale Fueling of Early Supermassive Black Holes and Little Red Dots
- Search for subsolar primordial black holes in low mass-ratio binaries with LIGO-Virgo O2 data and implications for the primordial black hole dark matter fraction
BibTeX
@misc{fakhry2026primordial,
title = {{Primordial Black Hole Seeds for Little Red Dots in $f(R)$ Gravity}},
author = {Saeed Fakhry},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2608.29727},
eprint = {2608.29727},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.29727},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Primordial Black Hole Seeds for Little Red Dots in f(R) Gravity
AU - Saeed Fakhry
PY - 2026
DA - 2026/10/26
PB - arXiv
DO - 10.48550/arxiv.2608.29727
UR - https://arxiv.org/abs/2608.29727
AB - The little red dots (LRDs) discovered by the James Webb Space Telescope host black holes of up to 10^9 M_⊙ within the first billion years, posing a challenge to conventional seeding scenarios. We investigate whether such seeds can form in dense clusters of primordial black holes (PBHs), in which the central object grows by gravitational capture of the surrounding PBHs while accreting gas, within Hu-Sawicki f(R) gravity, where the scalar field acts on the matter surrounding the PBHs. For the adopted cluster configuration, our results show that accretion and mergers reinforce one another: for time-averaged Eddington ratios λ_Edd≳0.3, the seed consumes its cluster by z≃5.5-$7.3$ and subsequently grows into the LRD mass range. Calibrated on the observed black-hole mass function, the model reproduces the abundance of LRDs near the peak of their population without further adjustment, while it underpredicts the abundance at z≃7.5 and overpredicts it at z≃2. Our findings indicate that the earliest seeds may accrete about twice as efficiently as later ones, and that the finite cluster reservoir can imprint a lower edge on the mass function near the cluster mass. Within the adopted screening and halo-growth prescriptions, the scalar field enhances the abundance of active seeds by up to ∼ 13% at lower redshifts and by ∼ 7% at z ≃ 7.5 for the strongest model considered, modestly moving the high-redshift prediction towards the data at fixed normalization. Also, the remnant spins can further discriminate between feeding modes.
ER -