The Andromeda–Milky Way collision is a galactic collision predicted to occur in about 4.5 billion years between the two largest galaxies in the Local Group the Milky Way, which contains the Solar System and Earth and the Andromeda Galaxy.

The Andromeda is approaching our Milky Way at nearly a quarter million miles per hour. It is the closest major galaxy to our Milky Way and is the most distant thing you can see with the naked eye. it is at a distance of 2.5 million light-years away from us. Absolute chaos will begin as the two galaxies approach each other, eventually becoming Milkomeda. Everything will look like a massive pinball game, with huge amounts of rocks, dust, asteroids, planets, and stars being thrown in all directions through the cosmos that we would see easily.

Until 2012, it was not known whether the collision was going to happen or not. After that researchers, using Hubble to track the motions of stars in Andromeda with unprecedented accuracy concluded that the galaxies would collide in about 4 billion years. Such collisions are relatively common, considering galaxies’ long lifespans. The remnant will look like a giant elliptical galaxy, which is a blob-like galaxy without discernible spiral arms or an internal structure.

Andromeda galaxy contains about one trillion stars and the Milky Way contains about 300 billion. The stars involved are sufficiently far apart that it’s highly improbable that any of them will individually collide. For example, the nearest part of the Sun is Proxima Centauri, which is about 4.2 light years away. If the Sun were a ping pong ball, then Proxima Centauri would be a pea about 680 miles away. Although stars are more common near the centers of each galaxy, the average distance between stars is still 100 billion miles. That is like placing one ping-pong ball every two miles; thus, it’s extremely unlikely that any two stars from the merging galaxy would collide, but some stars might be ejected.

The Milky Way and Andromeda each contain a central supermassive black hole. These black holes will eventually spiral into one another and converge near the center of the newly formed galaxy over a period that may take millions of years. When the supermassive black holes come within one light year of another, they will begin to strongly emit gravitational waves that will radiate further orbital energy until they merge completely. Gas taken up by the combined black holes could create an active galactic nucleus. If this happens it would release an inconceivable amount of energy.

Based on current calculations, scientists predict a 50% chance that in a merged galaxy the solar system will be swept out three times farther from the galactic core than its current position. Our galaxy is organized into spiral arms and the Sun is in a branch called the Orion Spur. If we were to be flung farther out, that means our solar system would land just at the fingertips of this arm. Scientists also predict sometime during the collision, there is a 12% chance that the solar system could be entirely ejected from the newly formed galaxy. For some reassurance, humanity would be long gone by then, of course. Such an event would have no adverse effect on the solar system and the chances of any sort of disturbance to the Sun or planets themselves may be remote, that is excluding planetary engineering.

By the time the two galaxies collide, the surface of the Earth will have already become far too hot for liquid water to exist, due to the gradually increasing luminosity of the Sun, ending all terrestrial life, but our planet will still be caught in the middle of this collision and its view of the universe will never be the same. If we could however see the night sky still, whether from the hellish perspective of Earth or the far reaches of the outer solar system, Andromeda would be growing larger in the sky, and eventually about 4 billion years from now, it could stretch from horizon to horizon like a serene rainbow of dew.

Our findings are statistically consistent with a head-on collision between the Andromeda galaxy and our Milky Way galaxy,” said Roeland van der Marel of the Space Telescope Science Institute (STScI) in Baltimore.