A candidate supermassive black hole in a gravitationally-lensed galaxy at z10

While supermassive black holes (BHs) are widely observed in the nearby and distant universe, their origin remains debated with two viable formation scenarios with light and heavy seeds. In the light seeding model, the first BHs form from the collapse of massive stars with masses of 10-100 \ M_, while the heavy seeding model posits the formation of 10^4-5 \ M_ seeds from direct collapse. The detection of BHs at redshifts z10, edging closer to their formation epoch, provides critical observational discrimination between these scenarios. Here, we focus on the JWST-detected galaxy, GHZ 9, at z10 that is lensed by the foreground cluster, Abell 2744. Based on 2. 1 Ms deep Chandra observations, we detect a candidate X-ray AGN, which is spatially coincident with the high-redshift galaxy, GHZ 9. The BH candidate is inferred to have a bolometric luminosity of (1. 0^+0. 5-₀. ₄) 10^46 \ erg \ s^-1, which corresponds to a BH mass of (8. 0^+3. 7-₃. ₂) 10⁷ \ M_ assuming Eddington-limited accretion. This extreme mass at such an early cosmic epoch suggests the heavy seed origin for this BH candidate. Based on the Chandra and JWST discoveries of extremely high-redshift quasars, we have constructed the first simple AGN luminosity function extending to z10. Comparison of this luminosity function with theoretical models indicates an over-abundant z10 BH population, consistent with a higher-than-expected seed formation efficiency.