In just a few billion years the closest galaxy to Earth, the Andromeda Galaxy, and the Milky Way will collide. In astronomical terms it will be a clash of the titans; but in human terms it is a slow process indeed. The two galaxies are two and a half million light years away from one another at present. The “clash” ahead is still about four billion plus years away in the distant future. In essence, expanding star systems reach a point in their expansion where they bounce back toward one another due to gravitational effects.
The Andromeda Galaxy has been moving toward the Milky Way for several billion years already. It surges at 250,000 miles per hour. At these speeds, the collision will reshape both galaxies as seen from planet Earth. At present both are spiral galaxies directly aimed toward one another. When they meet they are predicted to merge into less flat, and more elliptical, shapes. As both galaxies are assumed to have dense black holes at their center core, it is also predicted that the resulting compressed gas will create the fiery spectacle of new stars being born. This is already observed to be taking place in several even farther away galaxies, resulting in what is known as Supernovae.
It is within an exploding supernova that nuclear fusion occurs. Bright, bluish white tendrils of light are seen in known supernovae, such as the Crab Nebula and the Cygnus Loop. These results are called supernova remnants, occurring when shock waves heat the stellar matter within collisions. These types of magnificent explosions produce heavy elements, such as the iron found in human blood. This is just one significant outcome of what happens when galaxies collide.
The collision, based on Einstein’s famous theory of relativity; predicts that both considerably huge galaxies will produce gravitational radiation and gravitational waves that are responsible for such massive stellar shows. Also, in ongoing creation, is the matter and continually changing configuration of the known universe.
Each of these two galaxies contains the nearly unfathomable number of more than 100 billion stars. That is an astonishing amount of energy. Nevertheless, due to the equally amazing vast distances between all of these stars, most of both galaxies contains empty space. Most stars, then, will move right past each other in the “collision.”
Both galaxies, at present, are the familiar spinning, spiral galaxies people most typically imagine when they envision a galaxy. New shapes are being created all the time, of course, and galaxies shift and change to many shapes. Among these are the ever-popular spiral, the lenticular, the irregular and the elliptical. An elliptical galaxy can be thought of as a more three-dimensional version of the spiral galaxy.
The collision of galaxies appears ongoing and integral to formation of stars, their solar systems, planets and ultimately all life as it is known to exist. In which case, there is nothing to fear from the clash of such titans.