Galactic cannibalism is the process by which a larger galaxy merges with and absorbs a smaller galaxy, gradually incorporating its stars, gas, and dark matter into the larger system. This occurs when galaxies pass close enough for gravitational forces to strip material from the smaller galaxy, often forming tidal tails, streams, or shells as the stars and gas are redistributed.
Over time, the smaller galaxy is completely assimilated, contributing to the growth of the larger galaxy’s stellar mass and central bulge. Galactic cannibalism is most common in dense environments, such as galaxy clusters, where interactions are frequent, but it can also occur in more isolated regions. The process plays a key role in the hierarchical formation of galaxies, helping explain why massive galaxies, like elliptical galaxies, often contain stars from multiple progenitor galaxies.
Observational evidence of galactic cannibalism includes stellar streams around galaxies, distorted shapes, and unusually large central regions in galaxies that indicate past mergers. Simulations show that repeated mergers over billions of years shape the structure, morphology, and dynamics of galaxies, contributing to the evolution of the cosmic web.
In essence, galactic cannibalism is a cosmic growth process, where larger galaxies feed on smaller ones, driving galaxy evolution and contributing to the hierarchical buildup of structures in the universe.