Around 5 billion years from now. at about the time the sun is bloating into a red giant and eating the inner solar system, the Andromeda galaxy will come stomping up to the Milky Way and tear it to shreds. Andromeda will get badly mangled as well; the two galaxies will throw a fair deal of their mass out into interstellar space, but the bulk will merge into a new more massive galaxy. Individual starts are vanishingly unlikely to collide, though gravitational interactions with close passes will probably disrupt many planetary systems. Entire solar systems will be flung into the depths of interstellar space. Imagine how a civilization might evolve on a planet circling such a star… tens of millions of years after the event, the only lights in the night sky would be other planets, moons, asteroids… and one faint smudge that is the combined galaxy. *If* powerful telescopes are developed (and they might well not be, especially if there are no other planets), then the other galaxies throughout the universe might be detected, but it’s incredibly unlikely that they’ll be understood. With only a single star visible, how would these hypothetical astronomers ever even *hope* to grasp what galaxies are?
A computer simulation of the merger.
[vimeo 106350053]