Extreme properties of a compact and massive accreting black hole host in the first 500 MyrTripodi, Roberta (Avtor) Martis, Nicholas S. (Avtor) Markov, Vladan (Avtor) Bradač, Maruša (Avtor) Rihtaršič, Gregor (Avtor) Harshan, Anishya (Avtor) Judež, Jon (Avtor) Felicioni, Giordano (Avtor) astrophysicsearly universegalaxiessupermassive black holesLittle red dots (LRDs) are a high redshift galaxy population. Despite their high number densities, their nature is still uncertain. Here we present CANUCS-LRD-z8.6, a spectroscopically confirmed little red dot at a spectroscopic redshift of $z_{\mathrm{spec}}=8.6319$, hosting an active galactic nucleus. Its spectrum exhibits broad H$\beta\lambda$4863 Å emission, high-ionization lines (C iv, N iv]), high electron temperature, which are indicative of active galactic nucleus activity, and low metallicity ($Z$ < 0.1-0.2$Z_{\odot}$). The inferred black hole mass, $M_{\mathrm{BH}}=1.0^{+0.6}_{-0.4} \times 10^8 \mathrm{M}_{\odot}$, poses strong constraints on current black hole formation models and simulations. Additionally, its black hole is over-massive relative to its host, deviating from local $M_{\mathrm{BH}}-M*$ relations, suggesting an early, rapid black hole growth preceding that of its galaxy. CANUCS-LRD-z8.6 may represent an evolutionary link between early massive black holes and the luminous quasars observed at $z=6$.20252025-11-21 12:01:20Članek v reviji176105sl