Alma and the Subaru telescope on the trail of the enigmatic killers of Urgalaxes

almost a century ago, Edwin Hubble opened the realm of galaxies to us by showing it mists in the astronomer’s famous catalog Charles Messiersuch as Messier 31 and Messier 87were actually objects outside The Milky Way and that they must therefore be like the Universes, in the sense of Edge in a pamphlet from 1755, that is, sets ofstars identical to star system as we call the Milky Way, our galaxy.

M31 and M87, also known as Andromeda galaxies and Virgo A, is what is known to be from works of The Irish astronomer Lord Rosse in the middle of the 19the century, examples of spiral galaxies 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 depleted in these materials and where star formation is weak.

Jean-Pierre Luminet, Research Director at CNRS, and Françoise Combes, Professor at the Collège de France, talk to us about black holes, especially the large supermassive black holes in galaxies, which lie behind quasars and which affect the evolution of galaxies. © Hugot Foundation at the College de France

A joint development of supermassive black holes and galaxies

It will also take a long time for Messier and Rosse to discover that the M87 and the Milky Way contain supermassive black holes and that it is such a general situation as the division of galaxies into two main classes, namely spirals and ellipticals. However, in many cases there is a relationship of proportionality between the mass of a galaxy and the mass 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 connection between the growth processes in galaxies and those in the supermassive black holes they contain, as well as a causality relationship between the presence of these monsters and the death of the galaxies.

However, nothing is quite clear yet on all these topics, even if the paradigm for the growth of galaxies in a decade 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, we can already observe dead elliptical galaxies where stars no longer form, but we do not really know why certain galaxies are already depleted of molecular gas at the origin of star formation and others are not. . However, it is believed that this has something to do with the activity of supermassive black holes that accumulate matter and produce in response win substances and explosions of radiation that emit the gas and dust they contain.

That 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 freely consulted arXiv. It comes from the work of an international team of researchers led by Kei Ito in Sokendai, Japan, who used the database for Cosmic evolutionary study (Cosmos), an astronomical study designed to study the formation and evolution of galaxies as a function of both cosmic time (redshift) and the local environment of galaxies. The study covers an equatorial field of 2 square degrees with spectroscopy and imagery extending from the domain of X-rays to the waves radio thanks to most major telescopes space and a variety of large telescopes on earth. More than 2 million galaxies have been discovered, covering 75% of the ageUniverse.

Correlations already exist 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 seen by the world’s largest telescopes, includingAtacama 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 underway and those where star formation has stopped.

To achieve the goal they had set, astrophysicists also needed data collected within X-rays and waves radiobut as these data were much noisier and degraded, it was necessary to exploit them, have a larger number of observations, and low 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 domains, scientists have for the first time connected emissions in these last two domains of galaxies 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 galaxy’s stars alone, indicating the presence of an active supermassive black hole.

We then see clearly that galaxies with a giant black hole that is not very active, therefore collect some matter and as a result must produce a slight radiation eruption (remember that according to the laws of electromagnetic field the waves it can form carry light the amount of movement as substance particles in a gas stream), are also those where star formation is significant.

We see just as clearly that an abrupt end to star formation inUniverse primordial is correlated with increased activity of supermassive black holes. In a statement from the Subaru Telescope, Kei Ito summarizes the situation as follows: We have successfully discovered the activity of black holes 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 for understanding why they stop their star formation. This suggests the possibility that supermassive black holes are preventing 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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