The influence of galactic black holes extends beyond their host galaxy

Current galactic models admit the existence of supermassive black holes located at the center of each galaxy of sufficient mass. For several years, astrophysicists have been studying and modeling the effects of these black holes on their host galaxy; an essential component to the evolution of large galaxies in the Universe. Recently, a team of researchers took this study outside the galactic center to show that the influence of the black hole extends beyond the host galaxy.

At the heart of almost all sufficiently massive galaxies is a black hole whose gravitational field, although very intense, affects only a small region around the center of the galaxy. Even though these objects are thousands of millions of times smaller than their host galaxies, our current view is that the Universe can only be understood if the evolution of galaxies is regulated by the activity of these black holes, because without them the observed properties of galaxies cannot be explained.

Theoretical predictions suggest that as these black holes grow, they generate enough energy to heat up and chase gas inside galaxies over great distances. Observing and describing the mechanism by which this energy interacts with galaxies and modifies their evolution is therefore a fundamental question in current astrophysics.

With this in mind, a study carried out by Ignacio Martín Navarro, researcher at theInstituto de Astrofísica de Canarias (IAC), went further and tried to see if the matter and energy emitted around these black holes can alter the evolution, not only of the host galaxy, but also of the satellite galaxies which surround it, to even greater distances.

A notable influence of the central black hole on satellite galaxies

To do this, the team used the Sloan Digital Sky Survey, which allowed them to analyze the properties of galaxies in thousands of groups and clusters. The conclusions of this study, which began during Ignacio’s stay at the Max Planck Institute for Astrophysics, are published in the journal Nature.

Graph showing the variations in star formation rate in satellite galaxies as a function of their orientation relative to the central black hole of the host galaxy. © Ignacio Martín-Navarro et al. 2021

Surprisingly, we found that satellite galaxies formed more or less stars depending on their orientation relative to the central galaxy. », Explains Annalisa Pillepich, researcher at the Max Planck Institute for Astronomy (MPIA, Germany). To try to explain this geometric effect on the properties of satellite galaxies, the researchers used a cosmological simulation of the Universe called Illustris-TNG whose code contains a specific way of handling the interaction between central black holes and their galaxies. hosts.

As with observations, the Illustris-TNG simulation shows a clear modulation of the rate of star formation in satellite galaxies according to their position relative to the central galaxy. “. This result is doubly important, as it gives observational support to the idea that central black holes play an important role in regulating the evolution of galaxies, which is a fundamental characteristic of our current understanding of the Universe.

Better understand the interactions between black holes and galaxies

Nonetheless, this assumption is continually challenged, given the difficulty of measuring the possible effect of black holes in real galaxies, rather than just considering the theoretical implications. These results therefore suggest that there is a particular coupling between black holes and their galaxies, through which they can expel matter at great distances from galactic centers, and can even affect the evolution of other nearby galaxies.

So not only can we observe the effects of central black holes on the evolution of galaxies, but our analysis paves the way for understanding the details of the interaction. », Concludes Navarro.

Sources: Nature

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