Interactions between galaxies are quite normal, especially between giant and satellite galaxies. Two galaxies are drawn together by forces they can’t see but they can feel.
It’s a mutual gravitational attraction. Because of this, galaxies come too close to one another, to the point where the gravity of the satellite galaxy will attract one of the giant galaxy’s primary spiral arms.
They can’t do anything about it. As time goes on they grow closer and closer until they collide. Collisions may lead to mergers. Thus, assuming that neither galaxy has enough momentum to keep going after the collision has taken place. If one of the colliding galaxies is much larger than the other, it will remain largely intact and retain its shape, while the smaller galaxy will be stripped apart and become part of the larger galaxy.
What Happens After The Collision?
Some stars will be thrown out of the galaxy, others will be destroyed as they crash into the merging supermassive black holes. And the delicate spiral structure of both galaxies will be destroyed as they become a single, giant, elliptical galaxy. But as cataclysmic as this sounds, this sort of process is actually a natural part of galactic evolution.
Will Our Galaxy Collide In The Future?
The Andromeda Galaxy is approaching the Milky Way at about 110 kilometers per second (68 mi/s) as indicated by blueshift. It was Edwin Hubble, that in 1929 revealed observational evidence which showed that distant galaxies were moving away from the Milky Way. This led him to create Hubble’s Law, which states that a galaxy’s distance and velocity can be determined by measuring its redshift, a phenomenon where an object’s light is shifted toward the red end of the spectrum when it is moving away.
Such collisions are relatively common. Andromeda, for example, is believed to have collided with at least one other galaxy in the past, and several dwarf galaxies such as Sgr dSph is currently colliding with the Milky Way and being merged into it.
A tragic inevitable dance, isn’t it?