Black holes have an unexpected effect beyond their own galaxies, reveals study

There is a black hole at the center of practically every suitably massive galaxy, and its gravitational field. While known for being extraordinarily intense, they only impacted a tiny region surrounding the galaxy's center.

Even though these objects are millions of times smaller than their host galaxies, it was believed that the Universe can only be understood if the evolution of galaxies is regulated by the activity of these black holes, because the observed properties of the galaxies cannot be explained without them.

According to theoretical expectations, as these black holes increase in size, they generate enough energy to heat up and force out the gas within galaxies to tremendous distances. Observing and characterizing the mechanism by which this energy interacts with galaxies and changes their evolution is interesting. 

A study led by Ignacio Martn Navarro, a researcher at the Instituto de Astrofísica de Canarias (IAC), went a step further and attempted to determine whether the matter and energy emitted from around these black holes can affect the evolution of not only the host galaxy, but also the satellite galaxies around it, at even greater distances.

To accomplish this, the researchers employed the Sloan Digital Sky Survey, which allowed them to examine the features of galaxies in thousands of clusters. "Surprisingly we found that the satellite galaxies formed more or fewer stars depending on their orientation with respect to the central galaxy", says Annalisa Pillepich, co-author of the paper and researcher at the Max Planck Institute for Astronomy (MPIA, Germany).

To try to explain this geometrical effect on the features of the satellite galaxies, the researchers employed Illustris-TNG, a cosmological simulation of the Universe whose code includes a unique approach of dealing with the interaction between central black holes and their host galaxies. "Just as with the observations, the Illustris-TNG simulation shows a clear modulation of the star formation rate in satellite galaxies depending on their position with respect to the central galaxy", adds Pillepich.

This finding is significant because it provides empirical evidence for the assumption that core black holes play a major role in regulating the evolution of galaxies, which is a fundamental component of our present view of the Universe. Nonetheless, given the difficulties of measuring the possible effect of black holes in real galaxies rather than examining solely theoretical implications, this concept is constantly questioned.

These findings imply that there is a specific link between black holes and host galaxies, allowing them to expel matter to enormous distances from galactic centers and even influence the evolution of other neighboring galaxies.