Black holes fascinate theoretical physicists because they probably represent a theory of quantum gravity and probably also a unified theory of matter, and forces such as the hydrogen atom and the study of thermal radiation in the equilibrium of a black body were instrumental in the discovery of quantum mechanics.
Black holes suggest a holographic theory of reality and a deep and mysterious role of quantum information at the root of reality.
For astrophysicists, it’s something different, especially when it comes to supermassive black holes. It appears to be found in all large galaxies and there is a connection between their masses and those of the host galaxies, suggesting common growth processes. To understand how galaxies evolve, we need to understand how supermassive black holes also evolve.
Clearly there are matter accretion processes in both cases, and we are therefore trying to better understand how this happens in supermassive black holes. We also know that active galactic nuclei can emerge from these black holes, emitting radiation by becoming quasars, for example, as well as winds of matter that influence the galaxies in which these compact stars – which can contain at least a million solar masses – are found become.
Jean-Pierre Luminet, research director at CNRS, and Françoise Combes, professor at the Collège de France, tell us about black holes, especially the large supermassive black holes in galaxies that are behind quasars and influence the evolution of galaxies. © Hugot Foundation of the Collège de France
A nearby active galaxy discovered in 1975
Alma has just made a spectacular zoom in on an active galactic nucleus, as explained in a paper published in Science and a version of which can be found open access on arXiv. The network of radio telescopes of the Atacama Large Millimeter/submillimeter Array (Alma) has actually been used to uncover the secrets of a very special galaxy, namely the Compass Galaxy, which can be observed in the direction of the constellation of the same name with a simple telescope such as the Unistellar eVscopes.
Surprisingly, despite its proximity to the Milky Way, which is about 13 million light-years away, the Compass Galaxy was only discovered in 1975, although it is also a type II Seyfert galaxy, i.e. a spiral galaxy with a particularly bright and compact core (it). were named after the American astronomer Carl Seyfert, who studied these objects in the 1940s. The reason for this is that this galaxy is observed only 4 degrees below the galactic plane, making it difficult to detect as it is almost obscured by the Milky Way.
The international team of researchers led by Japanese astronomer Takuma Izumi from the National Astronomical Observatory of Japan (NAOJ) captured images with a light-year resolution of the center of the Compass Galaxy, highlighting gas streams in different phases. that is, in the state of molecules, of individual neutral atoms, but also of a fourth state of matter, the plasma, a mixture of ions and electrons.
A river of recycled material around a black hole
Basically, the simplest model of the accumulation of matter around a supermassive black hole (without going into details with a possible dust torus) involves the formation of a disk of matter that falls spirally towards the horizon of the black hole’s events.
The coils of matter rub together due to the viscosity of the gas, releasing heat and therefore radiation before the distance is reached where stable orbits no longer exist and the matter must inevitably fall into the black hole.
We had an idea of the rate of absorption of matter by supermassive black holes to ensure their growth, but at least in the case of the central black hole of the Compass Galaxy, thanks to the magnifying and resolving power of “Alma”, we discovered that the flow of gas passing through the disc fell was 30 times higher.
All observations and measurements in this specific case show that most of the gas is ejected perpendicular to its accretion disk by the accretion and radiation activity of the black hole. However, because gravity is strong, the streams of matter fall back onto the disk, completing a cycle. The matter is therefore recycled several times through this cosmic fountain process before finally falling into the black hole.
For Takuma Izumi: “The detection of accretion flows in a region just a few light-years from the actively growing supermassive black hole, especially in multiphase gas, and even the deciphering of the accretion mechanism itself are monumental achievements in the history of supermassive black hole research .” Phenomena. To fully understand the growth of supermassive black holes throughout cosmic history, we need to study different types of more distant supermassive black holes. This requires high-resolution, high-sensitivity observations, and we have great expectations for the continued use of Alma and next-generation large radio interferometers. “.