Formation timescale of high-redshift supermassive black holes

Determine whether standard astrophysical formation and growth mechanisms can produce supermassive black holes with masses of about 10^9 solar masses by redshift 7–9 within the available cosmic time, or whether such objects require primordial black hole seeds that predate galaxy formation.

Background

Observations reveal supermassive black holes (SMBHs) with masses ∼10^9 solar masses at redshifts around 7–9, including red galaxies with central SMBHs in this range and a highly luminous AGN at z ∼ 7. These findings challenge the timing and growth rates expected from conventional stellar remnant seeds and accretion models.

The authors explicitly state that it is unclear whether such SMBHs can form quickly enough under standard assumptions, raising the possibility that their seeds—or the SMBHs themselves—could be primordial, forming before galaxies. Resolving this would inform the origin of high‑redshift SMBHs and the role of PBHs in early structure formation.