Collision between Milky Way and the Andromeda

There are billions and billions of galaxies in the observable universe or say the total number of galaxies is impossible to count. So it is very obvious that in such a wide universe two galaxies will collide. The collision is a very obvious and common event in astronomy, whether it is between two galaxies or any other two bodies. Gravitational pull is the main reason for the collision.

            A similar collision is about to happen with our home galaxy. A head-on collision of the Milky Way will happen with the Andromeda Galaxy. The first evidence of collision appears when the spectrum observation of our neighbour galaxy showed the blueshift, which means the galaxy is approaching us and is most likely to collide with our home galaxy. Astronomers first thought that Andromeda will not collide with the Milky Way. It appeared that the galaxy is moving towards a point nearly 178,000 light-years away from the Milky Way. But after studying the relative motions of stars in the Andromeda galaxy, it was certain that the collision will happen after 4 billion years. 

            The collision will not be a sudden process. Both the galaxies will take around 2 billion years to completely merge under their gravitational influence and reshape into a new distorted or elliptical galaxy, known as the Milkomeda Galaxy. Andromeda is approaching us at a speed of 130 km/hr. Even when the two giant galaxies are colliding, the chances of stars within them colliding is very negligible. The MilkyWay has 300 billion stars and Andromeda has 1 trillion stars, but still, they are less likely to collide because of the very large distance between them. For example, Proxima Centauri, the nearest star to the Sun is about 4.2 light-years away, which is about 42 trillion kilometres!

            During the collision, there is a 50% chance that it will affect the Solar System. The worst scenario would be the solar system getting kicked out of the Milky Way and becoming the part of newly formed Milkomeda Galaxy. The probability of such an event is only 12%. Even in such a case, there will be no effect on the orientation of plants and our Sun. All the planets will still continue to revolve around the Sun with the same speed and in the same manner as they are doing today. 


            Due to the presence of a large amount of hydrogen in the disks of both galaxies, there is a high probability that the collision will trigger the formation of new stars. Hence there will no hydrogen left in the disks after the collision. Both the galaxies have Super-Massive Black Holes at their centre. So there is also a strong chance of both the SMBHs collide and merge into a single black hole. This will result in a release of an excessive amount of energy equivalent to 100 million supernovae explosions.

            We all know that in a few billion years our Sun will run out of hydrogen. This will lead to the expansion of the Sun. Hence by the time collision between two galaxies happens, there will be no existence of the Earth. All the terrestrial life would be already over. Even if the Earth survives, it will be a hot fireball with no life or water. Hence all we can do it to just make predictions about the collision, as no human will be there to witness the collision. However, we can observe Andromeda approaching us. As the Andromeda will continue to approach us, it will become brighter and brighter in the night sky

            Even if humans make their way to Mars and colonize there, by that time the excess heat from the Sun will make life impossible there too. So humanity has no chance to witness this beautiful collision unless we find some other way to colonize very far from the Sun. 

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