A dusty compact object bridging galaxies and quasars at cosmic dawn

Understanding how super-massive black holes form and grow in the early Universe has become a major challenge^1,2 since it was discovered that luminous quasars existed only 700 million years after the Big Bang^3,4. Simulations indicate an evolutionary sequence of dust-reddened quasars emerging from heavily dust-obscured starbursts that then transition to unobscured luminous quasars by expelling gas and dust⁵. Although the last phase has been identified out to a redshift of 7.6 (ref. ⁶), a transitioning quasar has not been found at similar redshifts owing to their faintness at optical and near-infrared wavelengths. Here we report observations of an ultraviolet compact object, GNz7q, associated with a dust-enshrouded starburst at a redshift of 7.1899 ± 0.0005. The host galaxy is more luminous in dust emission than any other known object at this epoch, forming 1,600 solar masses of stars per year within a central radius of 480 parsec. A red point source in the far-ultraviolet is identified in deep, high-resolution imaging and slitless spectroscopy. GNz7q is extremely faint in X-rays, which indicates the emergence of a uniquely ultraviolet compact star-forming region or a Compton-thick super-Eddington black-hole accretion disk at the dusty starburst core. In the latter case, the observed properties are consistent with predictions from cosmological simulations⁷ and suggest that GNz7q is an antecedent to unobscured luminous quasars at later epochs.