Giant black holes at the center of galaxies affect star birth

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[EN VIDÉO] Closer to black holes
Dive into the heart of black holes, these stars that consume all matter and even light!

With several millions, even billions of plenty sun, the supermassive black holes is located in the center of large galaxies. That The Milky Wayour galaxy, is home to e.g. Sagittarius A*, whose very first photo was recently revealed! Although we do not yet understand how they form, we do know how to study their impact on their environment. This is what an international team ofastronomers who was particularly interested in the beams of particles they emit when accreted from fabric. Their findings were published in the journal Natural astronomy

Jets hit the galactic disk

They targeted the galaxy IC 5063, located 156 millionlight years of the earth. Trapped by Hubble Space Telescope in 2019, its image is most curious: scientists describe an alternation between light areas and shadow areas, corresponding to twilight rays on earth. Everything appears to emanate from the core of the galaxy as if projecting rays of light that were either transmitted, therefore visible, or absorbed by clouds molecular, therefore invisible. But this phenomenon remains unusual because these beams of light coming from the heart of the galaxy actually correspond to jets emitted by the supermassive black hole that is there.

As the black hole inevitably attracts matter that gets too close to it, it deforms, falling toward it in a spiral. What is called a then occurs accretion disk, consisting of all this matter, which gradually falls towards the horizon of the astronomical monster. The different layer of the accretion disk does not spin at the same time velocityso that because of the friction gas heated and ionized. Electromagnetic radiation, even beams of ionized matter, is then emitted by the plasma of the disk, sometimes making it particularly luminous: in this case we are talking about quasar, for quasi-star. These rays are emitted perpendicular to the plane of the accretion disc, around which there is a torus of dust.

An artist’s impression explaining the unified AGN model. In any case, it is a supermassive black hole surrounded by an accretion disk, itself surrounded by a huge torus of dust and gas. Beams of particles are emitted, and by observing an AGN parallel to one of these beams, a very luminous blazar is obtained. At right angles, the perceived radiation is less intense and we see mainly a radio source. Between the two, and when the activity is very strong, it is a quasar. © NRAO Outreach

They could trigger star formation

Propelled at high speed in the galaxy, these jets exert an influence on the matter they then traverse. It is this effect that the research team wanted to investigate, targeting IC 5063. Because, in its case, the jets are emitted by the black hole in a different direction than the one normally encountered. In fact generally these jets of supermassive black holes are emitted perpendicular to the galactic disc, while for the galaxy IC 5063 they propagate in the plane of the galactic disc and therefore directly affect the clouds in the interstellar medium. The transition between dark and bright regions spans nearly 36,000 light-years, suggesting that the jet emitted by the central black hole’s accretion disk extended at least that far.

To learn more about these mysterious clouds that darken the galaxy, the team modeled several linesemissions through observations made by VLT and Alma: that of carbon monoxide (CO), from cation formylium (HCO+), from sulphur ionized andnitrogen ionized. This enabled them to calculate the densities and temperatures within molecular clouds and the medium through which the ray passes, so as to derive the conditions for pressure.

“We performed several thousand astrochemical simulations to cover a wide range of possibilities that may exist in IC 5063”said Thomas Bisbas, co-author of the study and researcher at the University of Cologne. “In this way, we were able to achieve the optimal combination of parameters physical clouds in different places in the galaxy »added Georgios Filippos Paraschos, co-author of the study and PhD student at the Institute Max Planck of radio astronomy in Bonn (Germany).

From these simulations, they were able to establish several pressure maps: that which prevails in the molecular clouds and the pressure that surrounds them. But when a sufficient density is reached in a molecular cloudcan it end up contracting and then becoming… a star ! “Our results show that supermassive black holes, even if they are located at the center of galaxies, can influence star formation on a galactic scale.said Professor Kalliopi M. Dasyra, first author of the study. Studying the effect of pressure changes on cloud stability was key to the success of this project. When a couple of stars actually form in one wind galactic, it is usually very difficult to detect their signal above that of all the other stars in the galaxy that host the wind. »

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