This is a big universe, but galaxies often collide. They don't smash together like cars, and I don't know that many stars actually ram into each other, but when galaxies get close, their gravity pulls each other out of shape. Complex deformations occur in the spirals and pressure waves set off new areas of star formation, astronomical fireworks displays occurring over millions of our years. Sometimes the two galaxies merge and regain a "traditional" whirling galaxy shape. This has happened many, many times and some astronomers think that even our galaxy may have collided with and absorbed another galaxy. We astronomy fans are also told that in a few billion years, our Milky Way will approach and collide with its neighbor, the Andromeda Galaxy, and will make a lot of cosmic noise, which only the mathematical spirits will hear.
"Galactic Collision" is acrylic on illustration board, 16" x 20", January 1991.