Collision Course 
Our home galaxy, the Milky Way, is on a collision course with another spiral galaxy. They’ll slam into each other in about four billion years, and eventually stir together to form a rather dull place containing perhaps a trillion stars.
Our partner in this galactic pile-up is M31, the Andromeda galaxy. It’s in the eastern sky on September evenings, and to the unaided eye looks like a small, faint, fuzzy blob of light.
M31 is moving toward us at about 250,000 miles an hour. It’s about two-and-a-half million light-years away, though, so the motion is imperceptible. Yet over the eons, M31 will grow ever larger in Milky Way skies as the two galaxies are pulled together by their powerful gravity.
As they merge, giant clouds of gas and dust will ram together and give birth to millions of new stars. The existing stars will be thrown into new orbits that buzz about the cores of the two galaxies like angry bees, while some stars are thrown into intergalactic space. The stars are all so far apart, though, that it’s unlikely that any of them will collide with each other.
After a couple of billion years, the combined galaxies will settle into a new galactic form — a fat, fuzzy football known as an elliptical. With most of its gas and dust gone, the combined galaxy will give birth to few new stars. Instead, its vast population of stars will grow old and faint — and over billions of years more, the giant galaxy will slowly fade away.
Script by Damond Benningfield, Copyright 2012