What exactly happens when two galaxies collide?
Collisions of galaxies are tremendous things (a galaxy is a LOT bigger than anything on Earth that you can imagine colliding!) and generate a lot of energy, heating and mixing up the gases in the two galaxies, making a good place for star formation. Unlike car collisions, galaxies collisions take a very long time – as many as a billion years or more for large galaxies! There is lots of interesting information to be found on the web about what happens when galaxies collide, and even some recent images of galaxies that are in the process of colliding. A good brief explanation and images can be found at: http://astrowww.phys.uvic.ca/~patton/openhouse/collisions.html Or, you can take a look at the NASA press release from a Hubble Space Telescope image of two galaxies colliding at: http://pao.gsfc.nasa.gov/gsfc/weekly/1997picks/97-138P.htm Galaxy collisions are complex interactions and there are many people trying to figure out how galaxies interact when they get close enough together, and
