Bigger Galaxy Eats Smaller Neighbor

Mr.Happy3050 writes "CNN is reporting here that the large galaxy Centarus A absorbed a smaller neighboring galaxy 200-400 million years ago. The absorption created a line of blue stars thousand of light-years across."

Comments

Re:Question

[drudd]

The simplistic explanation doesn't take gravity into account. Think of it as ants walking around on the surface of a balloon which is being blown up.

So if the ants stand still, they all get further away from each other (the classic analogy).

Next level of complexity: the ants are walking around with some random direction and speed. Some will be getting closer to each other, as long as their velocity is greater than the spread of the balloon's surface between them (i.e. distance grows by one inch, but they walked an inch and a half, so the two ants are now half an inch closer than they were initially).

Now you add in gravity (I don't know how to express this with ants... let's just say they feel some desire to walk towards each other, and that desire is related to their distance). So nearby ants feel some force which causes them to walk towards each other. If they are sufficiently close, this force will cause them to move faster towards each other than the inflation of the balloon is moving them apart (as in the second case).

This is why the stars in galaxies don't fly apart as the universe expands. The gravitational force at those scales is much greater than the expansion.

Doug