According the the current model of the expanding universe, all objects apart from our galaxie appear to be receding from us. Does this mean that our galaxy (the Milkey Way) will NEVER encounter another galaxy?
Suppose that two galaxies are on a collision course-what would be the result? Would the two merge to form a larger galaxy? Or, would the interaction be that the individual stars would capture eachother, and form binary pairs?
How dense is matter in a galaxy anyway? Would we ven notice anything if our galaxy encountered another?
Finally, given the vastness of space, what is the probability of such a collision?:rolleyes:
Previous discussions in GQ:
When Galaxies collide!!
What percentage of stars collide when two galaxy’s collide?
And a couple of websites:
When Galaxies collide and What happens when two galaxies collide?
It has happened quite a few times. The cartwheel galaxy is an example of one galaxy crashing dead center of a second. As far as what happens to the constituent stars and planets, I suspect quite a few orbits would be affected but probably not as many collisions as you might expect, due to the vast distances between stars and planets.
I think that several instances of galaxies colliding have been studied already. They do a sort of mashing smear from gravity, but they are not particularly dense so stars and such rarely collide directly (but some do, I mean with zillions of stars…). I don’t think that we would notice, we might have already passed through one already. It would take a good long time I think…
“The Milky Way is colliding with a small irregular galaxy right now!”
Also from the Bad Astronomy website:
“For September, 2002, they (the Heritage Project) put up a picture of Hoag’s Object (pronounced “Hoe Ag”), a fantastic ring galaxy. Evidently it suffered a massive collision with another galaxy, and the interaction of gravitational forces molded the galaxy into a giant hoop over a hundred thousand light years across.”
Well it appears that the universe is expanding, but that doesn’t impact what local conditions exist. In our case, the local cluster of galaxies are all gravitational bound together. The expansion simply makes the distance between these mass clusters increase.
Our own galaxy is currently devouring/colliding with several dwarf galaxies. The difference is that if one galaxy is sufficiently large the collision winds up being a merger.
As for density, 100 Billion stars of 1 solar mass over a disc 100 000 lyrs wide and 10 000 lyrs thick gives about 1 solar mass per 1000 cubic light-years (which seems low to me but we’re roughing it here.)
As for how often…not sure but they are not so uncommon that we’ve never seen them. http://antwrp.gsfc.nasa.gov/apod/colliding_galaxies.html
It’d be better to ask what’s the chance of a galaxy colliding with your house!!
Read about it, here, here, and here.
Peace
“Honey, what’s a galaxy doing in our living room?”
It seems like a galaxy collision, since there are extremely few stars actually colliding, would not have a significant loss of energy. It seems to me that many stars would have their motion messed with, but the center of masses of the two galaxies would continue, hardly changed. Why am I wrong?
And the thought of two stars from different galaxies actually colliding head-on is too cool to find words for.
You’re forgetting about the gravity. Each galaxy gravitationally affects the other.
I hate it when someone links to my site before I can. 
Galaxies collide all the time. We’re colliding with one (at least one!) right now, and many galaxies appear to have suffered collisions in their past. For example, the Andromeda galaxy appears to have two nuclei; one may be left over from a previous collision (though I am not up on the latest work on this, so take that with a grain of salt). I do know that many very large elliptical galaxies appear to have several nuclei, indicating many collisions. These tend to be at the centers of clusters of galaxies, which makes sense: the massive galaxies will tend to be in the center, and there are statistically more galaxies in the centers of clusters, so collisions are more common.
HA! I knew I’d seen it recently.
CurtC ask and yea shall recieve.
http://www.ifa.hawaii.edu/~barnes/research/stellar_collisions/index.html
Ther is a Java simulation of 2 colliding galaxies you might want to try at http://burro.astr.cwru.edu/JavaLab/GalCrash/GalCrash.html
Also there is a much better commercial simulation program available from www.virtualstar.co.uk but it costs £29
As an astronomer working in this sort of field, I’ll concurr with the Bad Astronomer. Galaxies collide all the time - generally in the core of clusters of galaxies, where the gravtational potential well is strong enough to draw less massive galaxies from the outskirts of the cluster in towards the centre, where they tend to collide and eventually merge with the largest galaxy in the cluster (the cluster dominant galaxy).
And when you get two clusters merging, you get even more galaxies colliding with each other.
In fact, the galaxy I’m working on at the moment has not one, but two galaxies colliding and merging with it.
Oh, and Bad Astronomer, you’re correct in thinking that post-collision galaxies tend to contain more than one nucleus, well, that’s at least what one of my colleagues has shown recently.
Not only can it happen, not only is it happening now, but it’s going to happen to our own Milky Way! In about 3 billion years, The Milky Way and Andromeda will collide!
The enterprising businessman should be able to find a way to milk this. I’m thinking along the lines of Galactic Collision Insurance. 'Scuse me while I print up some pamphlets.
It should be quite spectacular, pity we won’t be around to witness it, and the merger may well ignite the black hole at the galactic centre into a radio loud phase, which’ll be interesting…
It’s not the center of mass of the galaxies changing that’s important. If you look at a collision of two galaxies (There are simulations of colliding galaxies I’ve seen on the web) some of the stars from the two galaxies gain momentum and get ejected. The remaining stars lose momentum (on average, at least) so those stars of the two galaxies can form into a single galaxy.