Astronomers have found strong evidence that collisions between galaxies can “activate” supermassive black holes at their centers, turning once-quiet giants into bright, energetic engines called active galactic nuclei (AGN). Using data from the European Space Agency’s Euclid space telescope and advanced artificial intelligence tools, researchers report that merging galaxies are far more likely to host an AGN than solitary ones.
How Galaxy Collisions Feed Black Holes
According to two preprint studies, in most galaxies, supermassive black holes are quiet; however, when a large amount of gas and dust falls onto them, the falling material forms a hot accretion disk that brightens intensely and can release powerful jets. Such a phenomenon is what astronomers call an active galactic nucleus.
While examining approximately one million galaxies photographed by Euclid, scientists employed AI to determine which galaxies are undergoing mergers and which have AGN. They discovered that merging galaxies possess the probability of being active two to six times higher than that of non-merging ones; thus, the result serves as evidence that the gravitational havoc of a collision can propel gas inside the galaxy core to feed the black hole.
Why This Matters for Galaxy Evolution
Understanding what triggers AGN is key to piecing together how galaxies and their central black holes grow together. By releasing heat and gas, active black holes can starve star formation in their host galaxies and so change their future drastically. Even though it has been suggested that mergers may not be the cause of each AGN, this new data demonstrates that interactions between galaxies are the principal cause of the high-energy and luminous black hole activities that can be detected in the universe.
