2024NatAs...8..126B

Observations of quasars reveal that many supermassive black holes (BHs) were in place less than 700 Myr after the Big Bang. However, the origin of the first BHs remains a mystery. Seeds of the first BHs are postulated to be either light (that is, 10-100 M_⊙), remnants of the first stars, or heavy (that is, 10-10⁵ M_⊙), originating from the direct collapse of gas clouds. Here, harnessing recent data from the Chandra X-ray Observatory, we report the detection of an X-ray-luminous massive BH in a gravitationally lensed galaxy identified by the James Webb Space Telescope at redshift z ≈ 10.3 behind the cluster lens Abell 2744. This heavily obscured quasar with a bolometric luminosity of ∼5 × 10⁴⁵ erg s^–1 harbours an ∼10⁷-10⁸ M_⊙ BH assuming accretion at the Eddington limit. This mass is comparable to the inferred stellar mass of its host galaxy, in contrast to what is found in the local Universe wherein the BH mass is ∼0.1% of the host galaxy's stellar mass. The combination of such a high BH mass and large BH-to-galaxy stellar mass ratio just ∼500 Myr after the Big Bang was theoretically predicted and is consistent with a picture wherein BHs originated from heavy seeds.