The Dual Nature of GHZ9: Coexisting AGN and Star Formation Activity in a Remote X-ray Source at Z=10.145

We present JWST/NIRSpec PRISM spectroscopic characterization of GHZ9 at z= 10.145 ± 0.010, currently the most distant source detected by the Chandra X-ray Observatory. The spectrum reveals several UV high-ionization lines, including CII, SiIV, [NIV], CIV, HeII, OIII], NIII], and CIII]. The prominent rest-frame equivalent widths (EW(CIV)≃65A, EW(HeII)≃18A, EW(CIII])≃48A) show the presence of a hard radiation field, while the analysis of line ratio diagnostics suggest this galaxy hosts both AGN and star-formation activity. GHZ9 is nitrogen-enriched (6–9.5 times solar), carbon-poor (0.2–0.65 times solar), metal-poor (Z = 0.01–0.1 Z_⊙), and compact (< 106 pc), similarly to GNz11, GHZ2, and recently discovered N-enhanced high redshift objects. We exploited the newly available JWST/NIRSpec and NIRCam dataset to perform an independent analysis of the Chandra data confirming that GHZ9 is the most likely JWST source associated to X-ray emission at 0.5-7 keV. Assuming a spectral index Γ = 2.3 (1.8), we estimate a black hole (BH) mass of 1.60 ± 0.31 (0.48 ± 0.09) × 10^8M_⊙, which is consistent either with Eddington-accretion onto heavy (≥ 10^6 M_⊙) BH seeds formed at z=18, or super-Eddington accretion onto a light seed of ∼ 10^2-10^4 M_⊙ at z = 25. The corresponding BH-to-stellar mass ratio M_BH/M_star= 0.33±0.22 (0.10±0.07), with a stringent limit >0.02, implies an accelerated growth of the BH mass with respect to the stellar mass. GHZ9 is the ideal target to constrain the early phases of AGN-galaxy coevolution with future multi-frequency observations.