Example: An Elongated Spiral

The adjacent image shows one of the longest galaxies known, the SBb barred spiral NGC 6872, as imaged by the European Southern Observatory. This is one of the largest barred spirals known, measuring 750,000 light years in length. It is thought that the shape has something to do with the interaction of NGC 6872 with the S0 galaxy IC 4970, which is just above the center of the picture. The upper left spiral arm shows an unusual amount of star formation, which accounts for its blue color (Ref). It is thought that this star formation is associated with the recent passage of IC 4970 through this region of NGC 6872 (Ref). NGC 6872 is about 300 million light years away, in the southern sky constellation Pavo (the Peacock).

Example: Stephan's Quintet
An extremely interesting example of possible galactic collisions can be seen in Stephan's Quintet, shown in the adjacent figure. This is a close grouping of the visual image of 5 galaxies (the cores of the 5 galaxies are the brightest spots in the image). Four of these galaxies are probably physically close because they have similar redshifts; the 5th - in the lower left - is probably just accidentally in the line of sight since it has a very different redshift. In this image, the 3 galaxies in the upper part of the image appear to be colliding with each other. Credit: Kitt Peak National Observatory.
Computer Simulations of Galaxy Collisions
The largest computers may be used to simulate the interaction of galaxies and the resulting distortions and star formation. Here are three MPEG movies and descriptive sound files showing computer simulations of colliding galaxies: The first two movies show encounters between equal-mass galactic disks with two different initial orientations of the disks. The third movie shows a simulated encounter between a gas-rich disk galaxy and a gas-poor dwarf galaxy. In all three movies only the motion of the gas is shown---the unseen dark matter influences the collisions through gravitational interactions, but does not show in the simulations. Thus, in the third movie only the disk galaxy is visible in the movie; the gas-poor dwarf galaxy is not seen directly. The color coding in all three movies represents intensity of star formation: red indicates high rates and blue denotes low rates of star formation.

Source: http://zebu.uoregon.edu/movie.html, where further details on these simulations may be obtained.