2023-11-07 07:41:50
Black holes fascinate theoretical physicists because they are probably for a theory of quantum gravity, and probably also for a unified theory of matter and forces like the hydrogen atom and the study of thermal radiation at the equilibrium of a black body were for 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 else, especially when it comes to supermassive black holes. It appears to be found in all large galaxies and there is a relationship between their masses and those of host galaxies, suggesting joint growth processes. So, to understand how galaxies evolve, we need to understand how supermassive black holes also evolve.
Clearly, in both cases, there are matter accretion processes and we are therefore seeking to better understand how it is done with supermassive black holes. We also know that these black holes can give rise to active nuclei of galaxies which emit radiation, for example by becoming quasars, as well as winds of matter which affect the galaxies where these compact stars – which can contain at least a million of solar masses – are found.
Jean-Pierre Luminet, research director at the CNRS, and Françoise Combes, professor at the Collège de France, tell us about black holes, in particular the large supermassive black holes in galaxies which are behind quasars and which impact the evolution of galaxies. © Hugot Foundation of the Collège de France
A nearby active galaxy discovered in 1975
Alma has just zoomed in spectacularly on an active galaxy nucleus, as explained in an article published in Science and a freely accessible version of which can be found on arXiv. The network of radio telescopesAtacama Large Millimeter/submillimeter Array (Alma) was in fact used to uncover the secrets of a very particular galaxy, it is the Compass galaxy, observable in the direction of the eponymous constellation with a simple telescope like the Unistellar eVscopes.
Surprisingly, despite its proximity to the Milky Way, approximately 13 million light years away, the Compass Galaxy was only discovered in 1975 even though it is also a Seyfert type II galaxy. , therefore a spiral galaxy with a particularly bright and compact core (they were named after the American astronomer Carl Seyfert, who studied these objects during the 1940s). The reason is that this galaxy is observed only 4 degrees below the galactic plane, which made it difficult to discover, being almost obscured by the Milky Way.
The international team of researchers, led by Japanese astronomer Takuma Izumi from National Astronomical Observatory of Japan (NAOJ), obtained images with a resolution of the order of a light year of the center of the Compass Galaxy, highlighting gas flows in different phases, that is to say at the state of molecules, of individual neutral atoms but also of a fourth state of matter which is plasma, a mixture of ions and electrons.
A flow of recycled material around a black hole
Basically, the simplest model of the accretion of matter around a supermassive black hole (without going into details with a possible dust torus) involves the formation of a disk of matter falling in a spiral towards the horizon black hole events.
The turns of matter rub together due to the viscosity of the gas, which releases heat and therefore radiation before reaching the distance where stable orbits no longer exist and the matter must necessarily 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 we discovered, thanks to the power of magnification and resolution of ‘Alma, that the flow of gas falling through the disk was 30 times higher.
All the observations and measurements in this specific case show that the majority of the gas is ejected by the accretion and radiation activity of the black hole perpendicular to its accretion disk. But gravity being strong, the currents of matter fall back onto the disk, completing a cycle. The matter is therefore recycled several times by this cosmic fountain process before finally falling into the black hole.
For Takuma Izumi : « Detecting accretion flows in a region only a few light years around the actively growing supermassive black hole, especially in multiphase gas, and even deciphering the accretion mechanism itself, are monumental achievements in the history of research on phenomena linked to supermassive black holes. To comprehensively understand the growth of supermassive black holes over cosmic history, we need to study different types of supermassive black holes located further away. This requires high-resolution, high-sensitivity observations, and we have high expectations for the further use of Alma and next-generation large radio interferometers. ».
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