Possible explanation to the mystery of the colossal growth of some black holes

As far as is known, black holes are formed from the catastrophic contraction of star nuclei, and their initial mass is between about 5 times and several tens of times the mass of the Sun. From their creation, they can engulf matter from its environment and increase mass. However, it has been very difficult to explain how they can grow to masses millions of times that of the Sun, and even more surprising, to the billions of times that of the Sun that some possess.

Through X-ray observations of galaxies and simulations with digital models on supercomputers, a team led by Fan Zou of Pennsylvania State University in the United States has found the most solid explanation to date of how supermassive black holes have been able to grow. so much. The reconstruction that the team has done covers 12,000 million years of history of the universe, from when its age was about 1,800 million years, to its current age of about 13,800 million.

The research carried out includes two studies, one of them recently published and the other still pending to be presented.

The team has determined that supermassive black holes grow through a combination of two main pathways. One of them is by swallowing cold gas from its host galaxy (a process called accretion). The other is by merging with other supermassive black holes when galaxies collide with each other.

In the first growth path, when the gas is dragged in a whirlwind of matter from which the hole is fed, the temperature of that matter increases greatly and very strong and typical X-ray emissions are produced. These emissions are the telltale fingerprint that allows its growth by accretion to be traced, as pointed out by W. Niel Brandt, from Pennsylvania State University and a member of the research team.

The study authors measured accretion-driven growth using X-ray sky survey data accumulated over more than 20 years from three of the most powerful X-ray observatories launched into space, as well as data from other observatories. In total, they measured accretion-driven growth in a sample of more than 8,000 fast-growing black holes.

As for the second growth path of supermassive black holes, that of mergers between them, the team used IllustrisTNG to track it, a set of supercomputer simulations that model the formation, evolution and merger of galaxies since shortly after the Big Bang. (the colossal “explosion” with which the universe was born) to the present.

On the left, image combining X-ray (blue) and optical (red, green and blue) observations and, on the right, gas column density simulated from cosmological simulations with IllustrisTNG. The observed X-ray emission comes mainly from accreting supermassive black holes, as shown in the artist’s illustration in the inset. (Image: F. Zou (Penn State) et al.; observations: The XMM-SERVS Collaboration; simulations: The TNG Collaboration; illustration: Nahks TrEhnl (Penn State). CC BY-NC-ND)

The researchers found that, in most cases, accretion was the process that dominated the growth of black holes. Mergers had a notable secondary contribution, especially in the last 5 billion years for the most massive black holes. In general, supermassive black holes of all masses grew much more rapidly when the universe was younger. Therefore, the list of supermassive black holes in the universe was already almost complete 7 billion years ago.

In the case of the supermassive black hole in the central zone of our galaxy, which has a mass “only” about 4 million times that of the Sun, the research indicates that most of its growth most likely occurred at a younger time. very late in the history of the universe.

The first study published by the team in this line of research is titled “Mapping the Growth of Supermassive Black Holes as a Function of Galaxy Stellar Mass and Redshift.” And it appears in the academic journal The Astrophysical Journal. (Fountain: NCYT by Amazings)