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Published on: September 28, 2018
Primordial-Black-Hole-Based Pathways to Little Red Dots
Valerio De Luca1, Loris Del Grosso1, Gabriele Franciolini2,3,4
1Johns Hopkins University, William H. Miller III Department of Physics and Astronomy, 3400 North Charles Street, Baltimore, Maryland 21218, USA.
Physical Review Letters
|June 26, 2026
Summary
The James Webb Space Telescope discovered Little Red Dots (LRDs) with unexpectedly massive black holes (BHs). Primordial black holes (PBHs) are unlikely direct hosts, but mergers and gas accretion onto PBHs offer potential explanations for these early universe BHs.
Area of Science:
- Cosmology
- Astrophysics
- Galaxy Formation
Background:
- James Webb Space Telescope (JWST) observations reveal compact, high-redshift sources known as Little Red Dots (LRDs).
- These LRDs host supermassive black holes (BHs) disproportionately massive compared to their stellar content, challenging current galaxy formation models.
- The observed properties suggest LRDs might be an extreme class of early BH hosts.
Purpose of the Study:
- Investigate the potential primordial origin of supermassive black holes (BHs) observed in early universe LRDs.
- Evaluate the viability of primordial black holes (PBHs) as progenitors for the massive BHs in LRDs.
- Explore formation channels, including mergers and gas accretion, that could explain the observed BH properties in LRDs.
Main Methods:
- Rule out direct formation of observed BH masses in the early universe using cosmic microwave background (CMB) μ-distortion limits.
- Model the hierarchical mergers of lighter, observationally allowed primordial black holes (PBHs) to form massive BHs.
- Estimate gas accretion onto intermediate-mass PBHs while tracking metallicity evolution to match LRD properties.
Main Results:
- Direct formation of the observed BH masses in the early universe is excluded by CMB μ-distortion constraints.
- Hierarchical mergers of PBHs can form massive BHs but face challenges due to the rarity of required high-redshift dark matter halos.
- Gas accretion onto intermediate-mass PBHs, coupled with metallicity evolution, can reproduce the observed properties of LRDs within specific parameter spaces.
Conclusions:
- Primordial black holes (PBHs) are unlikely to form directly to the observed masses in LRDs.
- While PBH mergers are plausible, they struggle to explain the abundance of LRDs.
- Gas accretion onto intermediate-mass PBHs presents a viable channel for forming the massive black holes observed in Little Red Dots (LRDs), particularly in the lensed source QSO1.
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