A black hole in a near-pristine galaxy 700 million years after the Big Bang

Roberto Maiolino, Hannah Uebler, Francesco D'Eugenio, Jan Scholtz, Ignas Juodzbalis, Xihan Ji, Michele Perna, Volker Bromm, Pratika Dayal, Sophie Koudmani, Boyuan Liu, Raffaella Schneider, Debora Sijacki, Rosa Valiante, Alessandro Trinca, Saiyang Zhang, Marta Volonteri, Kohei Inayoshi, Stefano Carniani, Kimihiko Nakajima, Yuki Isobe, Joris Witstok, Gareth C. Jones, Sandro Tacchella, Santiago Arribas, Andrew Bunker, Elisa Cataldi, Stephane Charlot, Giovanni Cresci, Mirko Curti, Andrew C. Fabian, Harley Katz, Nimisha Kumari, Nicolas Laporte, Giovanni Mazzolari, Brant Robertson, Fengwu Sun, Bruno Rodriguez Del Pino, Giacomo Venturi

First listed 2025-05-28 | Last updated 2026-04-13

Abstract

The recent discovery of a large number of massive black holes within the first two billion years after the Big Bang, as well as their peculiar properties, have been largely unexpected based on the extrapolation of the properties of luminous quasars. These findings have prompted the development of several theoretical models for the early formation and growth of black holes, which are, however, difficult to differentiate. We report the metallicity measurement around a gravitationally lensed massive black hole at redshift 7.04 (classified as a Little Red Dot), hosted in a galaxy with very low dynamical mass. The weakness of the [OIII]5007 emission line relative to the narrow H$β$ emission indicates extremely low metallicity, about $4\times 10^{-3}$ solar, and even more metal poor in the surrounding few 100 pc. We argue that such properties cannot be uncommon among accreting black holes around this early cosmic epoch. Explaining such a low chemical enrichment in a system that has developed a massive black hole is challenging for most theories. Models assuming heavy black hole seeds (such as Direct Collapse Black Holes) or super-Eddington accretion scenarios struggle to explain the observations, although they can potentially reproduce the observed properties in some cases. Models invoking "primordial black holes" (i.e. putative black holes formed shortly after the Big Bang) may potentially explain the low chemical enrichment associated with this black hole, although this class of models also requires further developments for proper testing.

Short digest

JWST/NIRSpec-IFS dissects the triply imaged Little Red Dot Abell2744-QSO1 at z=7.04, isolating the narrow Hβ to map line ratios. [OIII]5007 is exceptionally weak—[OIII]/Hβn ≈ 0.6 within r<150 pc and <0.32 at 150–300 pc—implying Z ≈ 8×10^-3 Z⊙ centrally and Z<6×10^-3 Z⊙ in the extended gas, while broad Balmer lines/variability yield MBH ≈1.5×10^7 M⊙ in a host with Mdyn ≈10^7.1–10^8 M⊙. This places a massive black hole in an almost pristine, very low-mass galaxy only ~700 Myr post-Big Bang. The chemistry and mass budget strain heavy-seed or super‑Eddington growth paths, motivating alternatives such as primordial black-hole seeds that remain to be fully tested.

Key figures to inspect

• Fig. 1a–b: Spectral decomposition around Hβ/[OIII]; after subtracting the BLR and continuum, the plot shows strong narrow Hβ and strikingly weak [OIII]5007 that sets the low [OIII]/Hβn ratio.
• Fig. 1c: Annular (0.1″–0.2″ ≈150–300 pc) spectrum where narrow Hβ persists but [OIII] is formally undetected; this anchors the [OIII]/Hβn < 0.32 (3σ) limit and demonstrates extended low-Z gas.
• Fig. 1e: Radial profiles comparing narrow Hβ, broad Hβ, and continuum (PSF); reveals a compact core plus ∼300 pc extension of the narrow component, distinguishing NLR/SF-powered emission from the unresolved BLR.
• Fig. 2a–b: Metallicity calibrations place QSO1 at Z ≈ 8×10^-3 Z⊙ (central) and Z<6×10^-3 Z⊙ (outer); note how alternative high‑z calibrations would drive Z even lower and how [OII]/[SII] weakness rules out the high‑Z branch.
• Fig. 3: Position of QSO1 on metallicity vs MBH and MBH/M⋆ planes; illustrates the tension of a ~1.5×10^7 M⊙ accretor residing in a near‑pristine, very low‑mass host.