In a recent blog post, I discussed the collision between our Milky Way galaxy and the Andromeda galaxy. In about four billion years, the two vast, spiral shapes will combine and transform into a single elliptical galaxy via a powerful gravitational smash-up.
News of the awesome collision prompted many to ask about what happens to the stars within the galaxies. In particular, what might happen to our Sun and the planets around it.
The good news is that when galaxies collide, the stars inside them won’t crash together.
To understand why, one has to recognize just how far apart the stars are. It’s easiest to explain with a scale model.
Suppose the Sun were the size of a baseball. I live in Baltimore, so let’s imagine this baseball is located at home plate in Oriole Stadium.
One of the stars nearest our Sun is Alpha Centauri. Let’s also shrink that star down to a baseball for our scale model. The question is: where would the Alpha Cen baseball be located?
It would not be in the infield, or the outfield, or anywhere in the ballpark. It would not be in the city of Baltimore or even in the state of Maryland. For a correct scale model, the Alpha Cen baseball would be about 1,300 miles and many states away — in Houston, Texas.
One baseball in Camden Yards and one baseball in the Astrodome — that’s the relative size and separation of the stars in our part of the galaxy. You can see that there is a lot of space between Baltimore and Houston for other baseballs to pass through.
Hence when galaxies collide, the stars stream past each other at vast separations. The orbit of our Sun within the combined galaxy may change greatly, but the orbits of the planets around the Sun will not be affected.
One can rest easy knowing that our solar system will survive the great collision between the Milky Way and Andromeda. However, that doesn’t mean that the billion-year future of Earth is all rosy. There are other factors that will greatly alter our planet. I’ll discuss those in my next posting.