Small isolated galaxies hide hungry giant black holes!

In our universe, 80% of galaxies are concentrated in dense regions. The rest develop in nearly empty regions that extend hundreds of millions of light-years across and fill half of space. Galaxies are classified as isolated. Living their “life” free from outside interference. This is what interests astronomers who study them. Because they see an opportunity to learn more about the evolution of galaxies when they are almost undisturbed by the lack of an external event.

This is also the case for the supermassive black holes that hide in their hearts. They have, on paper at least, a few stars and gas at their disposal to feed on. However, according to work before James Madison University researchers (USA), meals of supermassive black holes at the center of isolated galaxies can, in some cases, be as abundant as those of their cousins ​​in more classical galaxies.

Black holes that thrive in the absence of competition?

Focusing on infrared emissions, the researchers studied several thousand galaxies. They show that isolates smaller than our own Milky Way are more likely to contain a supermassive black hole — what astronomers call an active galactic nucleus — than those in denser regions of the universe. For galaxies similar to our own or larger, the opposite is true.

The researchers see this as further evidence that the life cycle of galaxies in the empty regions of the universe is slowing down. Because fewer galaxies collide there, smaller galaxies take longer to merge into larger galaxies. In dense areas, the process has already taken place. The turmoil is already somewhat over. But the discovery still calls into question the role of galaxy collisions in the emergence of active galactic nuclei. It calls into question the fact that these collisions are necessary to trigger the phenomenon. Ultimately, the lack of competition may benefit these isolated supermassive black holes. No galaxy to feed them of course. But not to strip them of their gas either…