18 October 2019

The other day I read on the ABC website that our Milky Way galaxy is likely to be “eaten” by Andromeda.

If there’s one thing I can’t stand, it’s clickbait. No, we’re not all about to die.

First, it’s not expected to happen for another 4.5 billion years. So I wouldn’t be too fussed about it if I were you.

Second, galaxies might look pretty substantial, but honestly, they’re not. Probably the most crowded place I can think of in the current universe would be a globular cluster, such as Omega Centauri (this is my shot).

To give you an idea of how crowded these places are, Alpha Centauri, the closest star to the Earth, is about four light years away. The stars in a cluster like this are about one light year apart on average. Of course, in the densest part, they’re much closer - down to one light day apart.

Life as we know it (Jim) in there just wouldn’t be possible. Star collisions here are a genuine possibility. Not only that, any planet would be torn away from its star by intensely fluctuating gravity. To top it off, the cosmic radiation from all those stars would destroy any DNA or its equivalent. Not a friendly place.

So, what might happen when the Andromeda galaxy decides to knock on our door? Most of the stars, like those in the Milky Way, are very far apart, so probably the word “merge” would be better than “collide”. Imagine a ghost passing through a wall. The stars from Andromeda would pass by at a safe distance and have little effect on our solar system. Probably the worst thing that would happen is that the two galaxies will change shape and lose their nice spirals.

So the probability of the sun colliding with an incoming star, or of the Earth getting flung off into space would very low. Anyway, I can guarantee that you won’t be around to see it.

Galaxy image: JPL. Thanks to Ted Doboz from the Facebook Astronomy Club for technical advice.