What happens when galaxies collide? 

With billions of galaxies in our universe, it's no surprise that they sometimes collide. The Milky Way and its nearest similarly sized neighbor, Andromeda or M31, are part of the local group of galaxies. They're pretty close to each other. Only about 10 galaxy lengths separate the Milky Way and Andromeda. And when they collide in 4 billion years it will be spectacular. 

We can simulate the collision of the Milky Way and Andromeda galaxies and predict that it should lead to a great deal of new stars, and a whole lot of galactic chaos. Eventually, the two galaxies will merge into a single galaxy, which will settle down into a larger Milkdromeda Galaxy. But don't worry. The stars within the galaxies won't collide. 

Galaxies are made up of mostly empty space. And the stars within them are very spread out, but the gas that surrounds the stars and forms them will collide spectacularly. Many galaxies are in the middle of a collision today. These type of galaxies are the ones that would not have fit into Edwin Hubble's categories. Irregularly shaped spirals merging and distorting arms winding in strangely beautiful shapes. The exquisite detail of these types of collisions can be studied in a new light with NASA's James Webb Space Telescope.