An 800-million-solar-mass black hole in a significantly neutral Universe at redshift 7.5

TL;DR

This paper reports the discovery of a supermassive black hole in a quasar at redshift 7.54, providing insights into early black hole growth and the state of the intergalactic medium during reionization.

Contribution

First detection of a quasar at z=7.54 with a supermassive black hole, supporting models of rapid early black hole growth and probing the epoch of reionization.

Findings

Black hole mass of 8×10^8 solar masses at z=7.54

Significant neutral hydrogen fraction (>33%) during reionization

Evidence of a Gunn-Peterson damping wing indicating a neutral intergalactic medium

Abstract

Quasars are the most luminous non-transient objects known and as a result they enable studies of the Universe at the earliest cosmic epochs. Despite extensive efforts, however, the quasar ULAS J1120+0641 at z=7.09 has remained the only one known at z>7 for more than half a decade. Here we report observations of the quasar ULAS J134208.10+092838.61 (hereafter J1342+0928) at redshift z=7.54. This quasar has a bolometric luminosity of 4e13 times the luminosity of the Sun and a black hole mass of 8e8 solar masses. The existence of this supermassive black hole when the Universe was only 690 million years old---just five percent of its current age---reinforces models of early black-hole growth that allow black holes with initial masses of more than about 1e4 solar masses or episodic hyper-Eddington accretion. We see strong evidence of absorption of the spectrum of the quasar redwards of the Lyman alpha emission line (the Gunn-Peterson damping wing), as would be expected if a significant amount (more than 10 per cent) of the hydrogen in the intergalactic medium surrounding J1342+0928 is neutral. We derive a significant fraction of neutral hydrogen, although the exact fraction depends on the modelling. However, even in our most conservative analysis we find a fraction of more than 0.33 (0.11) at 68 per cent (95 per cent) probability, indicating that we are probing well within the reionization epoch of the Universe.