When two massive, gas‑rich galaxies merge, gravity drives vast amounts of cold molecular gas toward the centers of both systems, where supermassive black holes (SMBHs) reside. These brief, turbulent phases can light up one or both black holes as active galactic nuclei (AGN), making them some of the most energetic objects in the universe. Yet, puzzlingly, not all merging galaxies host two actively feeding black holes; some show only one, while others seem to have no appetite.


