How can galaxy encounters change a spiral galaxy’s structure?

Galaxy encounters significantly alter the structure and appearance of spiral galaxies through various gravitational and dynamical processes. These interactions are not rare; rather, they are fundamental mechanisms that drive galactic evolution.1

Key ways these encounters change a spiral galaxy include:

• Morphological Distortion: Collisions and tidal interactions frequently distort the shape of a galaxy, particularly its spiral arms. Tidal forces can create giant arcs of stars or long stellar tails, which serve as evidence of past encounters.12
• Gas Stripping and Star Formation: Violent interactions can sweep out a galaxy’s interstellar gas. Conversely, in regions where galaxies merge, the collision of gas and dust clouds can trigger intense bursts of star formation, leading to the creation of massive, luminous star clusters.31
• Structural Transformation: Frequent collisions in dense environments can transform a spiral galaxy into an S0 galaxy by depleting its gas and leaving behind only a gasless disk and a spherical component.3
• Accretion and Cannibalism: Through a process often called galactic cannibalism, larger galaxies capture and absorb smaller ones. The remnants of these "eaten" galaxies, such as star streams, often become integrated into the larger galaxy's structure.13