Question: According to your work,when two galaxies collide, they will merge into a single object in a long period. How does it related to our earth and will it happen to our galaxy?

Jillian Scudder answered on 18 Jun 2015:

It will happen to our galaxy! Our closest galaxy, Andromeda, is too big and too close to not collide with us, but we have a lot of time left before it gets here. Our galaxy and Andromeda should be a single object in about 4-5 billion years. The interesting thing about these collisions is that the stars in each galaxy don’t collide at all! They’re so small and there’s so much space between them that they all go past each other without hitting each other – it’s the gas in both galaxies that gets really hit by the other galaxy- and that just creates a bunch of bright new stars.