Question

Why is it possible for galaxies to merge but not stars?

Answer 1

A galaxy is made of roughly 100 billion stars. So you would think that in a head on collision between two galaxies, there would be countless collisions between those stars, right? The fact is that in such a collision, the probability of two stars colliding is almost 0 because most of the space in a galaxy is just vaccum and the density of stars is not very big since the galaxies are extremely big. In other words, the sizes of the stars are very small compared to the average distance between them. Thus galaxies can merge.

Whereas the space between stars is not empty infact it is full of gas and dust andmany other particles.This is the reason why cant a star merge with each other.