Interesting Astronomy story on BBC News today. Nice to see that Astronomy is still considered to be a "sexy" science: Which is probably due to images like this one.
That's what two galaxies look like when they collide. Pretty.
When I studied Astrophysics and Space Science at university (now TEN years ago - damn, that makes me feel old) it was never mentioned that the Milky Way was going to merge with the Andromeda galaxy - I presume it's a relatively recent discovery - but we were told about galaxy collisions, and their effects on galaxy shape and star formation.
Everybody is probably familiar with the classic spiral shape galaxy:
What you're probably not so familiar with are the other shapes, such as bar spiral:
And Irregular galaxies:
We still don't know a huge amount about how or why galaxies form into particular shapes, (Wikipedia has one of the easier to follow guides of our understanding so far) but both the Elliptical and Irregular type galaxies are thought to be formed by the collision of two (or more!) galaxies - which brings about the rather horrible concept of a so-called "cannibal" galaxy...
Because gravitation is such a long-ranged force, galaxies can affect each other over mind-bogglingly large distances (millions of light years). Galaxies which collide eventually form into huge super-galaxies, with so much mass that they can influence other galactic objects, meaning that these cannibal galaxies swoop around the intergalactic ether, gobbling up smaller (and thereby vulnerable) galaxies. Thankfully, this process takes billions of years to occur, but it must be absolutely cataclysmic for the galaxies involved. I can only imagine the destruction wreaked when this kind of thing happens.
Just be thankful that we're not due to hit Andromeda for another 5 billion years, eh?