Cosmologists have suspected this for a long time. After all, the Andromeda galaxy and the Milky Way galaxy are moving toward each other. However, it wasn't 100% certain that Andromeda would hit us head on rather than slipping past us. Well, those doubts have been laid to rest. Astronomers from NASA have confirmed that Andromeda will definitely collide with the Milky Way. Fortunately (or unfortunately, depending on your perspective), this won’t happen for about four billion years. To make matters more interesting, a third, much smaller galaxy, called the Triangulum galaxy may also join in the festivities.
About two billion years after the initial crunch, the two galaxies will combine into one large galaxy, as the following animation explains.
By the way, very few if any collisions between stars are expected to occur. Despite the vast numbers of stars in each galaxy, the amount of empty space is so large that no stars are likely to crash into each other. In fact, it’s very possible that our solar system will escape the event unscathed. Of course, the sun will be flung into a different region of the galaxy, which will undoubtedly have some consequences for anything still living on Earth. But then again, by that time, the sun will be well on its way to becoming a white dwarf, so a collision with another galaxy may be the least of Earth's problems.