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

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.

• The paper identifies a quasar with an 800-million-solar-mass black hole at redshift 7.5, evidencing rapid black hole growth in the early Universe.
• The authors employed advanced photometric and spectroscopic techniques across multiple telescopes to derive precise mass and luminosity estimates.
• The discovery challenges conventional models by suggesting early supermassive black hole formation in a largely neutral intergalactic medium.

Overview of the Discovery of a Supermassive Black Hole in a Neutral Universe

The paper "An 800-million-solar-mass black hole in a significantly neutral Universe at redshift 7.5" presents significant insights into the early Universe's cosmic formation and reionization period through the discovery of a high-redshift quasar, J1342+0928. This observation is pivotal, considering the quasar's location in a Universe that remained predominantly neutral at a redshift of 7.5.

This quasar, with an imposing bolometric luminosity of $4 \times 10^{13}$ times that of the Sun, and harboring a black hole of approximately $8 \times 10^8$ solar masses, provides compelling evidence for the existence of supermassive black holes during the Universe’s infancy, merely 690 million years post-Big Bang. The discovery, rooted in observations across various infrared and optical surveys such as ALLWISE, UKIDSS, and DECaLS, suggests the possibility of early massive black-hole growth, potentially requiring initial masses exceeding $10^4$ solar masses or phenomena like episodic hyper-Eddington accretion.

Detailed Analysis and Methodology

The detection criteria for identifying quasars at high redshifts required advanced methods due to the absorption by the intergalactic medium (IGM) rendering them mostly invisible to optical bands. The methodology leveraged high signal-to-noise imagery combined with specific wavelength detections, utilizing sophisticated photometric and spectroscopic techniques at facilities such as the Magellan, Large Binocular Telescope, and Gemini North telescopes to confirm the quasar as well as deduce its properties, including its systemic redshift of $z = 7.5413 \pm 0.0007$.

Parsing the emission line properties and employing Gaussian fittings, the researchers have echoed velocity offsets consistent with other high-z quasars, highlighting the quasar’s spatial and dynamic uniqueness within a rapidly evolving Universe. The bolometric luminosity and mass estimations, framed through the integration of power-law spectral emissions and balancing with potential systematic uncertainties rooted in local scaling relations, affirm the quasar’s Eddington accretion episode.

Implications for Early Universe Cosmology

The presence of such a supermassive black hole so early in cosmic history challenges existing paradigms of black-hole and galaxy co-evolution models, which traditionally struggle to explain rapid growth without invoking atypically massive seed black holes or enhanced accretion scenarios.

Further, the detection of the Gunn-Peterson damping wing suggests notable neutral hydrogen fractions ($x$ values), emphasizing observations within the epoch of reionization. With consistent implications for a neutral hydrogen fraction $>0.33$ at a 68% confidence level, these results provide crucial constraints on reionization timelines and the role of early cosmic structures in ionizing the Universe.

Future Directions and Theoretical Considerations

This research underscores the necessity of refining the models of early quasar environments and ionization structures and invites further spectroscopic endeavors to probe high-redshift quasars and ancillary absorption phenomena. Enhanced signal-to-noise ratios and broader spectral coverages may yield precise assessments of the IGM’s neutral fraction and systematically decipher the reionization energy budgets and dynamics.

In summary, the discovery and analysis of J1342+0928 offers a rich narrative into early cosmic evolution, challenging contemporary astrophysical models and encouraging detailed explorations of the nascent molecules and astronomical structures that shaped the neutral-to-ionized transition of the Universe. The work presented continues to push the boundaries of our understanding of the Universe's formative years, elaborating a timeline for reionization and conglomeration into the cosmic tapestry that we observe today.