Galaxy mergers occur when two or more galaxies collide and combine due to their gravitational attraction. This process can take millions to billions of years and often results in the formation of a larger galaxy. During a merger, the galaxies can distort each other's shapes, leading to the creation of new stars from the gas and dust involved. These events are common in the universe and can significantly influence the evolution of galaxies. For example, when the Milky Way merges with the Andromeda Galaxy in about 4.5 billion years, it will reshape both galaxies and create new stellar systems.