In the article published today in the Astronomy & Astrophysics journal, new evidence suggests how supermassive black holes, with masses of several billion times that of our Sun, formed so rapidly in less than a billion years after the Big Bang. The study, led by researchers of the National Institute for Astrophysics (INAF), analyses a sample of 21 quasars, among the most distant ever discovered, observed in the X-rays band by the XMM-Newton and Chandra space telescopes. The results suggest that the supermassive black holes at the centre of these titanic quasars, the first formed during the cosmic dawn, may have reached their extraordinary masses through very rapid and intense accretion, thus providing a plausible explanation for their existence in the early stages of the Universe.
Quasars are active galaxies powered by the central supermassive black holes (known as active galactic nuclei), which emit an enormous amount of energy as they attract matter. They are extremely luminous and distant from us. In particular, the quasars examined in this study are among the most distant objects ever observed, dating back to a time when the Universe was less than a billion years old.
In this work, the analysis of X-ray emissions from these objects revealed an entirely unexpected behaviour of the supermassive black holes at their centres: a connection emerged between the shape of the X-ray emission and the speed of the winds of matter ejected by the quasars. This relationship links the wind speed, which can reach thousands of kilometres per second, to the temperature of the gas in the corona, the region that emits X-rays closest to the black hole. Thus, the corona turned out to be connected to the powerful accretion mechanisms of the black hole itself. Quasars with low-energy X-ray emission, and thus a lower temperature in the corona, show faster winds. This indicates a highly rapid growth phase that exceeds a physical limit for the accretion of matter called the Eddington limit, which is why this phase is called "super-Eddington." Conversely, quasars with higher-energy X-ray emissions tend to exhibit slower winds.
"Our work suggests that the supermassive black holes at the centre of the first quasars formed within the first billion years of the Universe's life may have actually increased their mass very rapidly, challenging the limits of physics," says Alessia Tortosa, lead author of the study and researcher at INAF in Rome. "The discovery of this connection between X-ray emission and winds is crucial for understanding how such large black holes could have formed in such a short time, thus providing a concrete clue to solve one of the greatest mysteries of modern astrophysics."
The result was achieved mainly by analysing data collected with the XMM-Newton space telescope of the European Space Agency (ESA), which allowed for approximately 700 hours of observations of the quasars. Most of the data, collected between 2021 and 2023 as part of the Multi-Year XMM-Newton Heritage Programme, under the direction of Luca Zappacosta, a researcher at INAF in Rome, is part of the HYPERION project, which aims at studying hyperluminous quasars during the cosmic dawn of the Universe. The extensive observation campaign was led by a team of Italian scientists and received crucial support from INAF, which funded the program, thereby supporting cutting-edge research on the evolutionary dynamics of the early structures of the Universe.
"In the HYPERION program, we focused on two key factors: on one hand, the careful selection of quasars to observe, choosing the titans, meaning those that had accumulated as much mass as possible, and on the other hand, the in-depth study of their properties in X-rays, something never attempted before on such a large number of objects from the cosmic dawn," says Luca Zappacosta, a researcher at INAF in Rome. We hit the jackpot! The results we're getting are genuinely unexpected, and they all point to a super-Eddington growth mechanism of the black holes."
This study provides important insights for future X-ray missions, such as ATHENA (ESA), AXIS, and Lynx (NASA), which are scheduled for launch between 2030 and 2040. In fact, the results obtained will be useful for refining the next-generation observational instruments and for defining better strategies for investigating black holes and active galactic nuclei in X-rays at more distant cosmic epochs. These are key elements for understanding the formation of the first galactic structures in the primordial Universe.
Related journal article: " HYPERION. Shedding light on the first luminous quasars: A correlation between UV disc winds and X-ray continuum ", di Tortosa A. et al. 2024, Astronomy & Astrophysics.
