Galactic collisions are a common event that occurs throughout the universe. In fact, collisions between galaxies are a natural part of galaxy formation, and it is likely that all galaxies, including the Milky Way, have collided with one or more galaxies in the past. However, what about the future? Will the Milky Way ever collide with another galaxy in the future? As a result, our nearest galactic neighbor, the Andromeda Galaxy, is advancing toward us. At some point in the next five billion years, the Milky Way and Andromeda will collide.
How fast does Andromeda move?
Hubble image of two colliding spiral galaxies. NASA
When the collision between Andromeda and the Milky Way occurs will depend on how quickly the Andromeda galaxy is moving toward us. Although the Andromeda Galaxy is the largest galaxy closest to the Milky Way, it is still 2.5 million light-years away, so it still has a huge distance to travel. Current calculations place Andromeda’s speed at 68 miles per second (110 kilometers per second). This is tremendously fast, but given the distance between the Milky Way and Andromeda, it will be about five billion years before the two galaxies collide.
What will happen when the two galaxies collide?
A computer-generated image of how the Milky Way-Andromeda collision will start from Earth. NASA
Collisions between the Milky Way and Andromeda will develop in a manner similar to most other galactic collisions. As the two galaxies approach, the gravitational pull between them will distort their shapes and stretch their spiral arms. The Milky Way and Andromeda will cease to be spiral galaxies and instead appear to be more irregular galaxies. The gravitational dance between the two galaxies will last for many millions of years and the two galaxies will pass through each other several times. During the collision, it is very unlikely that one star will collide with another. The distances between the stars are simply too large for collisions to occur. However, nebulae can collide due to their larger surface area. When large clouds of hydrogen collide, a high rate of star formation will occur. In addition, the gravitational tidal forces between the Milky Way and Andromeda will ignite more star formation. The two galaxies will enter a phase called the stellar eruption phase. Countless stars will form in a relatively short period of time, and the process itself may even deplete the supply of usable hydrogen to both galaxies.
It is likely that a large number of stars will be expelled from both galaxies. Most of the other stars will probably be thrown into a completely different position. If our sun is still around when the Milky Way and Andromeda collide, it will probably be pushed toward the outer regions of the galaxy, and there is even a small possibility that our solar system may be ejected from the galaxy.
Eventually, the Milky Way and Andromeda will completely merge and become a single much larger galaxy. They will no longer have their spiral shapes and instead will probably form in an elliptical galaxy. Astronomers have named this theoretical galaxy Milkomeda.
Will the Earth be around?
Five billion years is a long time, and the collision itself will last many millions of years. Will the Earth and the solar system be around long enough to witness the collision between the Milky Way and Andromeda? It is estimated that the moment of the collision occurs at the same time as our sun will enter the final stages of its life. It is very likely that the sun still exists, but it will not be the sun to which we are accustomed. Rather, the sun will have evolved into a red giant star. The sun will become so large that it swallows the orbits of Mercury, Venus, and possibly Earth. Even if the Earth survives the red giant phase, the surface of our world will be too hot to support any form of life. The Earth will probably be around when the Milky Way and Andromeda collide, but unfortunately there will be no life forms to see it develop.
Aidan Remple June 23, 2022 in Science