almost a century ago, Edwin Hubble opened the realm of galaxies to us by showing that nebulae in the famous catalog of the astronomer Charles Messiersuch as Messier 31 and Messier 87were in fact objects external to the Milky Way and that they must therefore be like it Universe-islands, in the sense of Kant in a pamphlet of 1755, that is to say sets ofstars identical to star system which we call the Milky Way, our Galaxy.
M31 and M87, aka the Andromeda galaxies and Virgo A, are what are known to be from the works of Irish astronomer Lord Rosse in the middle of the 19the century, examples of spiral and elliptical galaxies respectively. But it will take longer to discover that if in the first case the galaxy still contains gas and dust in clouds molecules where star nurseries are formed, this is not the case in M87 which is impoverished in these materials and where star formation is weak.
Jean-Pierre Luminet, research director at the CNRS, and Françoise Combes, professor at the Collège de France, talk to us about black holes, in particular the large supermassive black holes of galaxies which are behind quasars and which impact the evolution of galaxies. © Hugot Foundation of the College de France
A joint evolution of supermassive black holes and galaxies
It will also take a long time after Messier and Rosse to discover that M87 and the Milky Way contain supermassive black holes and that it is a situation as general as the division of galaxies into two main classes, namely spirals and ellipticals. However, there is in many cases a relationship of proportionality between the mass of a galaxy and that of the supermassive black hole it hosts. and like the big ones elliptical galaxies are also devoid of gas and dust and that they contain three very large supermassive blacks, we suspect a relationship between the growth processes of galaxies and those of the supermassive black holes they contain, as well as a relationship of causality between the presence of these monsters and the death of the galaxies.
Nothing is however perfectly clear yet on all these subjects, even if for a decade the paradigm of the growth of galaxies via filaments of cold gases, channeled by filaments of dark matter, shed a bright light on them, as explained to Futura by cosmologist Romain Teyssier.
We note for example that not only more than 10 billion years ago can we already observe dead elliptical galaxies where stars are no longer forming, but we do not really know why certain galaxies are already emptied of molecular gas at the origin of star formation and others not. It is assumed, however, that this has something to do with the activity of supermassive black holes accreting matter and producing in response winds matter and blasts of radiation ejecting the gas and dust they contain.
The astrophysicists try to solve these puzzles in several ways and of course based on observations. We have further proof of this with an article published in The Astrophysical Journal, which can be consulted freely at arXiv. It comes from the work of an international team of researchers led by Kei Ito in Sokendai, Japan, which used the database of the Cosmic Evolution Survey (Cosmos), an astronomical survey designed to probe the formation and evolution of galaxies as a function of both cosmic time (red shift) and the local environment of galaxies. The survey covers an equatorial field of 2 square degrees with spectroscopy and imagery ranging from the domain of X-rays to that of the waves radio thanks to most major telescopes space and a number of large telescopes on the ground. More than 2 million galaxies are detected, covering 75% of the age of theUniverse.
Correlations already present 10 billion years ago
In this case, Ito and his colleagues used a sample of galaxies 9.5 to 12.5 billion miles away.light years of the Milky Way as seen by the world’s largest telescopes, including theAtacama Large Millimeter/submillimeter Array (Alma) and the Subaru Telescope. The team first used optical data and infrared to identify two groups of galaxies : those where star formation is in progress and those where star formation has stopped.
To achieve the goal they had set themselves, the astrophysicists also needed data collected in the field of X-rays and waves radiobut these data being much more noisy and degraded it was necessary to exploit them, to have a larger number of observations and to make averages to draw a clearer and usable signal.
By combining observations of galaxies already identified in the visible and infrared with those in the X and radio domain, the researchers have for the first time associated emissions in these last two domains to galaxies located more than 10 billion light-years away. We can then see galaxies containing supermassive black holes associated with galaxies with or without star formation because the X-ray and radio emissions are too strong to be explained by the stars of the galaxy alone, indicating the presence of a active supermassive black hole.
We then clearly see that galaxies with a giant black hole that is not very active, therefore accreting little matter and having to produce a weak blast of radiation as a result (remember that according to the laws of electromagnetic field the waves it can form carry light amount of movement like particles of matter in a flow of gas), are also those where star formation is significant.
We see just as clearly that an abrupt end to star formation in theUniverse primordial is correlated with increased activity of supermassive black holes. In a statement from Subaru Telescope, Kei Ito summarizes the situation as follows: We have successfully detected black hole activity inside dying galaxies, even in the distant Universe, by combining intensive observations from large telescopes around the world, including the Subaru Telescope. This result from observations is important to understand why they stop their star formation. It suggests the possibility that supermassive black holes prevent the growth of galaxies. However, we do not yet know the mechanism. To understand the process, the team will investigate further. »
Françoise Combes, professor at the Collège de France, talks to us in more detail about supermassive black holes. © Ecole Normale Supérieure, PSL
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