The high-redshift ($z>10$) galaxies GHZ9 and UHZ1 observed by the James Webb Space Telescope are very massive and exhibit exceptionally high black-hole-to-star mass ratios with the central black hole masses $M\gtrsim {10}^7{M}_{\odot }$. In this paper, we explore the possibility that these systems are seeded by the supermassive primordial black holes (SMPBHs), which came into being in the very early Universe, with initial masses $\sim {10}^7{M}_{\odot }$. We present the self-similar accretion solutions for SMPBHs, and find that the mass growth of SMPBHs during the pregalactic era may be negligible. These SMPBHs, when the redshift $z\lesssim 20$, can accelerate seeding high-redshift galaxies and their baryonic content, and consequently explain the central supermassive black holes (SMBHs) of high-redshift massive galaxies through sub-Eddington accretion. According to our results, SMPBHs could lead to the existence of more massive SMBHs at higher redshifts compared to other SMBH seed scenarios. In particular, observations of SMBHs with masses $M\gtrsim {10}^7{\mathrm{M}}_{\odot }$ at $z>20$ could serve as potential probes of primordial black holes.

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• Formation & evolution of stars & galaxies
• Galactic nuclei & quasars
• Primordial black holes