Constantly I am reading that the Andromeda Nebula Galaxy is barelling toward us and we will meet in so many billion years. But is this the whole truth or just one of those oversimplifications for stupid laymen? If it is coming toward us, then are we going toward it? Does it just look like it is approaching because both of us are going around with the general rotatation of the Local Group, and that causes an optical illusion, although I don’t see how.? There seems to be mixed feeling about whether the Local Group is rotating as a whole or not, but I think the consensus is that it must be, because everything is rotating. When, o when will someone make a computer simulation of the celestial mechanics of the Local Group and where everytrhing is going?
Andromeda is bigger than the Milky Way and is close enough that we are under the influence of its gravity. From an outside observors point of view the Milky Way is barrelling in on the Andromedan’s party. However, since we are stuck inside of the Milky Way it is much easy to say that Andromeda is coming closer to us.
Your wish is Discover’s command… sort of. If you go to the November 2000 issue and click on “R&D”, then “Collision Course,” you’ll see some still shots of a simulated collision between our galaxy and Andromeda.
Ever hear of relativity?
We don’t know if we’re going to collide with the Andromeda galaxy. That’s because it’s so darn hard to measure sideways speed. It’s simple to measure radial speed - you just use Doppler shifts (redshift/blueshift of light). And Andromeda does have a slight blueshift, indicating that it’s coming towards us (or we towards them). But are we on a collision course, or is it moving even faster sideways so we won’t meet at all? There’s no way to know. I mean, how would YOU measure sideways speed? Take a photo, take another photo 10 years later and see how much the galaxy has moved? You can do that for nearby stars, but not a distant galaxy.
Considering that the visible universe is expanding (per Hubble, contra Einstein) like a surface of a bubble in 4 (x-y-x-t) dimensional space, the chances of galaxies (the smallest form on the bubble surface) colliding is extremely remote.
OH MY GOD!!! IT’S COMING RIGHT AT US! AAAAAAAAAAAAAAAAAAH!
What? Billions of years, you say?
nevermind…
It’s also important to note that even if we do collide, it probably won’t have much effect on our Solar System or planet. Galaxies are mostly empty space, and can largely just pass right through each other.
DeutschFox, the expansion of the Universe is miniscule on the scales we’re talking about here. Collisions between galaxies actually turn out ot be fairly common.
Thanks Chronos … I’ve never personally seen two or more galaxies collide. I guess that my thinking on the expansion of the universe, based on Hubble, is that everything, particularly galaxies, are moving away from each other. I know you like to quote Einsteinism’s and he also disagreed with the Hubble’s concept of an expanding universe but was proven dead wrong. In fact, Einstein wasn’t right about any major scientific issue after 1915! How far back in time are the “galaxy” collisions you are referring to … it is possible that early formations 12 billion years ago did collide … but really, we got to “expand” our thinking … 
I believe the Hubble has taken some cool pictures of two galaxies colliding. I saw a photo in one of the online Hubble collections.
The photos are not loading, for some reason, however, a couple of the hypertext references on that page do link to photos that do load.
It’s a Shock-Wave® issue.
Here’s another link with many interacting galaxies:
I got more galaxies in collision!
Heck, there are even clusters of galaxies in collision!
And take a look at the Cartwheel Galaxy, colliding head-on with a smaller galaxy, causing shock waves to ripple out in all directions, just like a rock splashing in water. This titanic act is causing the deaths of millions of old stars and the creation of millions of new ones.
Please pass the vaseline! I guess the “Hubble Expansion” theory has some kind of holes in it. Hats of to all of you and a warm apology to Chronos … Andi
I assume that you mean that your personal “‘Hubble Expansion’ theory” has holes in it. The cosmological expansion model in no way disallows collisions between galaxies. Otherwise, given all that photographic evidence of galactic close-encounters, astronomers would be pretty stupid to believe in it, eh?
Huh? How?
From the website:
If I’m incorrect in concluding that the “ripple of energy” is the cause of the supernovae, I think you can see why I did so. And it would seem that in this example, a galactic collision most certainly could affect the individual stars. It must depend on the angle and velocity of the collision and how densely-packed the stars are.
Let me lay on you another awesome fact: The blue ring in the photo, which contains billions of new stars, is so large (150,000 light-years in diameter), it would encircle our entire Milky Way Galaxy.
Like Chronos and Podkayne said, galaxies can collide even though the universe is expanding. The expansion is only on immense scales. Although most galaxies (& galaxy clusters) are speeding away from ours, our Local Group of galaxies are gravitationally connected to each other such that they do not expand away from each other. Galaxy clusters are common.
IIRC, the Milky Way may already be colliding with 1 or 2 small galaxies (the Magellanic Clouds) and probably collided with others in the past. The Milky Way and the Andromeda Galaxies are the two largest in our Local Group & their collision could have little effect or could completely reshape both galaxies. It should at least trigger lots of new star formations.