Using years of Hubble Space Telescope observations, Harvard astrophysicists modeled the proper motion (the motion side to side) of Andromeda and found that a galactic collision is inevitable. Unlike the radial velocity, the proper motion must be calculated by comparing images taken at different times by Hubble to measure how far Andromeda has moved relative to background galaxies. They also note that the Solar System would likely be located on the outskirts of the new galaxy.
Although the thought of our galaxy smashing into another seems forbidding, our Solar System will almost definitely survive. Within galaxies, the stars are so far apart from one another that collisions between them are improbable. The spiral of the Milky Way and the ellipses of Andromeda will combine to form a giant elliptical galaxy astronomers call ‘Milkomeda.’ The formation will be far from instantaneous. As they get closer, tidal pull will begin to distort the galaxies. Within dense gas clouds, stars will form as the two galaxies simultaneously come together and fly apart as they settle into a single large galaxy. Though humans will not likely be around to witness the merger in 4 billion years, the cosmic light show that accompanies the birth of our new galaxy will be spectacular.