Effects of black holes reaching beyond their own galaxies

Satellite galaxies form more or fewer stars depending on their orientation with respect to the galaxy at the center, which in turn is affected by gas and energy expelled by their central black hole. This unexpected effect has been observed and analyzed by researchers from the Astronomy international centers.

At the heart of every sufficiently massive galaxy there is a black hole whose gravitational field, although very intense, affects a small region around the galactic center, although its effects can also go further.

When satellite galaxies exist, their evolution is conditioned by their interaction with the surrounding environment that surrounds the central galaxy, which in turn can be affected by gas and energy expelled by its central supermassive black hole. However, the nature of this coupling between black holes and galaxies is highly disputed and observational evidence is scarce.

To shed light on this relationship, an international study has analyzed whether the matter and energy radiated by black holes is capable of altering evolution, not just the host galaxy, but also from the farthest satellites.

The team has used the Sloan Digital Sky Survey mapping to analyze the properties of galaxies in thousands of groups and clusters; and the results of the study have now been published in the journal Nature.

“Surprisingly we have found that satellite galaxies form more or fewer stars depending on their orientation with respect to the central galaxy,” explains Annalisa Pillepich, researcher at the Max Planck Institute for Astronomy (MPIA, Germany) and co-author of the work.

Quenched galaxies on the minor axis of the central galaxy
The team has found that the ‘duller’ satellite galaxies are relatively less frequent along the minor axis of their central galaxies. This observation could seem contradictory, since the activity of black holes is expected to eject mass and energy preferentially in that direction.

However, the study shows that the anisotropic signal (with different physical properties depending on the direction in which it is measured) observed is precisely due to the nature of the feedback from black holes in the massive halos in the environment, in such a way that the flows Outlets driven by active galactic nuclei clear the surrounding environment, thus reducing star formation in satellite galaxies.

To try to explain this geometric effect on the properties of satellite galaxies, the scientists resorted to a cosmological simulation of the universe called TNG, which in its code implements a particular treatment for the interaction between black holes and host galaxies.

Union of simulations and observations
As in the observations, the TNG simulation shows a clear modulation in the star formation rate of satellite galaxies depending on their position relative to the central one.

The data therefore support the idea that black holes play an important role in regulating the evolution of galaxies, a fundamental pillar in the current understanding of the universe.

However, this hypothesis is continually questioned given the difficulty in, in practice, measuring the possible effect of black holes in real galaxies, beyond theoretical considerations.

The results of the study also suggest that there is a particular type of coupling between galaxies and black holes, by means of which they are capable of expelling material at great distances from the galactic centers, even altering the evolution of other nearby galaxies.

Beyond observing the effect of black holes on the evolution of galaxies, our analysis opens a door to understand the details of this interaction.

.Reference:  “Anisotropic satellite quenching modulated by black hole activity”. Nature, 2021