The Day Andromeda Came Crashing In

Worried about getting hit by a meteorite? Aw, that’s so boring. Just wait -- a few more billions of years, and we’ll have an entire GALAXY falling down on us!

‘Andromeda’ is the name of the incoming star system. And believe us, it’s not the sort of thing you easily shoot away with some rocket missiles. Think of a vast armada of some 300 billion massive stars and hundreds of billions of planets, hurtling towards us at the breathtaking speed of 300 kilometers per second. The Andromeda Galaxy is big enough to literally gulp down our entire Milky Way. It is HUGE, measuring some 150,000 light years across.

It will be quite a stir. Think of stars and planets flying about. Think of vast cosmic explosions. Think of gravitational ripples ploughing through your body, think of blasts of radiation flogging your planet. There will be choking, cosmic gas clouds everywhere, and supernova’s going off, and black holes roaming around. Everywhere you look, you’ll see explosions and violence. The sky will be `like a Christmas tree lighting up’, as one researcher put it.

And then, amidst all this cosmic rumble-a-bumble, there’s us. It is hard to tell what exactly awaits our tiny, little world, should it still exist. Perhaps our planet is swallowed by a black hole. Perhaps it gets incinerated in a supernova, or fried by a gamma ray burst. Or perhaps it'll be squashed by something far more mundane, like a rogue meteorite, or a simple, incoming sun-like object. There won't be any insurance guys left to make up for the damage, that's for sure.

Exit Milky Way: Artist's impression of our poor Milky Way, cleaved by Andromeda. In reality, both galaxies will be ripped apart (see below).

Luckily, the bad stuff won’t happen overnight. For starters, the Andromeda Galaxy is still very far away. Although Andromeda is already about six times larger than the full moon in the night sky (but much fainter), it should take something like 2 to 3 billion years before it comes crashing in. That should give us some head start to come up with something.

And even then, disaster will unfold only slowly. The distances in the Universe are simply too large for it to happen all at once. There will be many spectacular space explosions and crashes and outbursts around -- but only every now and then: say, once every so many thousands of years. All in all, it should take the Andromeda Galaxy something like 1 billion years to smash up our Milky Way completely.

For our planet and our Milky Way may go down, but out of the remains comes a brand new galaxy! It should be an elliptical star system, much like the one we’re living in now -- but much, much larger. There will even be lots of new, young stars around. They will light up in the dense parts of the space clouds.

That’s why scientists aren’t too gloomy. In general, they consider colliding galaxies as something beautiful. When galaxies crash into each other, it’s like they’re mating: out of the mayhem arises a youthful, brand new galaxy. And astronomers know what they’re talking about: they have studied several well-known colliding galaxies already, peeking through their telescopes.

So when Andromeda starts falling, just bear in mind: you might die -- but it’ll be a fun thing to see!

Andromeda Mishap: A computer model study of the collision of the Milky Way (the smaller galaxy) with Andromeda reveals how Andromeda plows into our star system like a saw (a-b), how both galaxies unravel (c-e) and finally merge again, forming a new galaxy (h). (Images with permission John Dubinski, University of Toronto)