INSTITUTE OF ASTROPHYSICS OF THE CANARY ISLANDS (IAC)
PICTURE: ARTISTIC COMPOSITION OF A SUPERMASSIVE BLACK HOLE THAT REGULATES THE DEVELOPMENT OF ITS ENVIRONMENT. Show more CREDIT: GABRIEL PÉREZ DÍAZ, SMM (IAC) AND DYLAN NELSON (ILLUSTRIS-TNG).
At the heart of almost every sufficiently massive galaxy is a black hole whose gravitational field, although very intense, only affects a small area around the center of the galaxy. Although 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 the galaxies is regulated by the activity of these black holes, because without them the observed properties of the galaxies cannot be be explained.
Theoretical predictions suggest that as these black holes grow, they generate enough energy to heat up and expel the gas in galaxies over great distances. Observing and describing the mechanism by which this energy interacts with galaxies and changes their evolution is therefore a fundamental question in astrophysics today.
With this aim in mind, a study led by Ignacio Martín Navarro, a researcher at the Instituto de Astrofísica de Canarias (IAC), went a step further and sought to investigate whether there was any matter and energy emitted by these black holes can change the development not only of the host galaxy, but also of the satellite galaxies surrounding it at even greater distances. 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 today in Nature magazine.
“Surprisingly, we found that the satellite galaxies formed more or fewer stars depending on their orientation in relation to the central galaxy,” explains Annalisa Pillepich, researcher at the Max Planck Institute for Astronomy (MPIA, Germany) and co-author of the article. To explain this geometric effect on the properties of the satellite galaxies, the researchers used a cosmological simulation of the universe called Illustris-TNG, the code of which contains a specific handling of the interaction between central black holes and their host galaxies. “As with the observations, the Illustris TNG simulation shows a significant modulation of the star formation rate in satellite galaxies as a function of their position in relation to the central galaxy,” she adds.
This finding is doubly important as it supports the observational assumption that central black holes play an important role in regulating the evolution of galaxies, which is a fundamental feature of our current understanding of the universe. Still, this hypothesis is constantly being challenged as it is difficult to measure the possible effect of black holes in real galaxies rather than just considering theoretical implications.
So these results suggest that there is a special coupling between the black holes and their galaxies, through which they can eject matter at great distances from the galactic centers and even affect the evolution of other nearby galaxies. “So we can not only observe the effects of central black holes on the development of galaxies, but our analysis also opens the way to understanding the details of the interaction,” explains Ignacio Martín Navarro, first author of the article.
“This work was made possible by the collaboration between two communities: the observers and the theorists who, in the field of extragalactic astrophysics, find that cosmological simulations are a useful tool for understanding how the universe is behaving,” he concludes.
Article: Ignacio Martín Navarro, Annalisa Pillepich, et al. “Anisotropic satellite extinction, modulated by black hole activity”. Nature, June 10, 2021. DOI: 10.1038 / s41586-021-03545-9