Galaxies across the observable universe are engaged in ultra-slow motion interactions with each other, close encounters, flybys, and sometimes collisions. The outcome may be different in every case.
Sometimes the presence of a neighboring galaxy's gravitational pull as it passes by can disturb, or harass, the processes of star and planet formation. In other cases genuine head-on collisions occur - except they're less of a collision and more of a gentle coalescence, a merger of two mighty clumps of matter into something new. This is the probable fate of our own Milky Way and our neighboring large spiral galaxy Andromeda - our mutual gravitational attraction is pulling us out of the cosmic expansion of space, turning us around and bringing us together in about 4 to 5 billion years time.
In other places though, close encounters of the galactic kind can effectively destroy a system. Gravitational tides can shred a galaxy, turning a hive of a hundred billion stars and gas into a torn and raggedy mess. But it can also create some of the most beautiful and strange cosmic forms, great disturbances like stellar paint splashed through the void.
The image above is a particularly striking one. In this new portrait by the Hubble Space Telescope the galaxy NGC 2936 is being pulled asunder by its close passage to the elliptical galaxy (lower) NGC 2937 to form what has been called 'the Penguin' (sometimes 'the Porpoise', or by the name Arp 142). With an eye made of the core galactic stars, and feathers of interstellar gas and dust, this is a zoomorphic beast you'd do well to steer clear of. But is it beautiful.
Here's a chart of the whole scene, with a scale.