Stellar Collisions
While the Andromeda Galaxy contains about one trillion (1012) stars and the Milky Way contains about three hundred billion (3x1011); the chance of even two stars colliding is negligible because of the huge distances between each pair of stars. For example, the nearest star to the Sun is Proxima Centauri, about 3x107 solar diameters (4x1013 km or 4.2 ly) away. If the Sun were a ping-pong ball in Paris, the equivalent Proxima Centauri would be a pea-sized ball in Berlin (and the Milky Way would be about 1.9x107 km wide, about a third of the distance to Mars).
Stars are much denser near the centres of each galaxy with an average separation of only 1.6x1011 km. But that is still a density which represents one ping-pong ball every 3.2 km. Thus, it is extremely unlikely that any two stars may collide.
Read more about this topic: Andromeda–Milky Way Collision