Galactic collisions are a common event that occurs in the universe. In fact, collisions between galaxies are a natural part of galaxy formation, and it is likely that every galaxy, including the Milky Way, has collided with one or more galaxies in the past. But what about the future? Will the Milky Way ever collide with another galaxy in the future? As it turns out, our nearest galactic neighbor, the Andromeda galaxy, is accelerating toward us. Sometime in the next five billion years or more, the Milky Way and Andromeda will collide.
How fast is Andromeda moving?
Hubble image of two spiral galaxies colliding. NASA
When the collision between Andromeda and the Milky Way occurs will depend on how fast the Andromeda galaxy moves toward us. Although the Andromeda Galaxy is the closest large galaxy to the Milky Way, it is still 2.5 million light-years away, so there is still a huge distance to cover. Current calculations set the speed of Andromeda at 68 miles per second (110 kilometers per second). This is extremely fast, but given the distance between the Milky Way and Andromeda, it will take about five billion years before the two galaxies collide.
What will happen when the two galaxies collide?
Computer generated image of what the beginning of the collision of the Milky Way and Andromeda from Earth will look like. NASA
The collisions between the Milky Way and Andromeda will develop in a manner similar to most other galactic collisions. As the two galaxies approach each other, 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 will instead look more like 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 many times. During a 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 huge clouds of hydrogen collide, this will result in a high rate of star formation. In addition, the gravitational tidal forces between the Milky Way and Andromeda will ignite further star formation. The two galaxies will enter a phase called a stellar eruption phase. Countless stars will form in a relatively short period of time, and the process itself may even deplete the reserves of usable hydrogen in both galaxies.
A large number of stars are likely to be ejected from both galaxies. Most of the other stars will probably be transferred to a completely different position. If our sun is still around when the Milky Way and Andromeda collide, it will probably be pushed into the outer regions of the galaxy, and there is even a small chance that our solar system will be ejected from the galaxy.
Eventually, the Milky Way and Andromeda will merge completely and become a single, much larger galaxy. They will no longer have their spiral shapes and will probably form into an elliptical galaxy. Astronomers have named this theoretical galaxy Milcomeda.
Will the Earth be around?
Five billion years is a long time, and the collision itself will last for many millions of years. Will the Earth and the solar system be long enough to witness the collision between the Milky Way and Andromeda? It is estimated that the time of the collision will occur at about the same time as our sun enters the last stages of its life. It is very likely that the sun will still exist, but it will not be the sun we are used to. Rather, the sun would have turned into a red giant star. The sun will become so large that it will swallow 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 sustain 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 watch it unfold.
Aiden Remple June 23, 2022 at Science
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