What will become of the Milky Way in the remote future? Will it become unstable or evolve into something different?
On its own, the Milky Way will not become unstable. It will continue to grow by cannibalising small galaxies like the Magellanic Clouds (currently, the Milky Way is swallowing a small dwarf galaxy).
However, the Andromeda galaxy (which is of similar size or larger than the Milky Way) is right now headed towards the Milky Way and will tidally interact (via gravity) or collide with the Milky Way after several billion years. Some day, the two galaxies will merge and may become an elliptical galaxy (like M87), or if the collision happens just right, will reform into an even bigger disk-shaped galaxy. However, these events will take place only after a VERY LONG time.
This page was last updated June 27, 2015.