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Originally Posted by Paintballr
Ah alright, but since we are kinda a sprial like a blender cause of that blade. Do we eventually get sucked into the center?
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The bar really has nothing to do with the fact that the galaxy rotates. All galaxies rotate around a center point if it's a spiral galaxy, elliptical galaxy or irregular galaxy. If they didn't, they'd all fly apart and they wouldn't exist. Part of the reason for the rotation is gravity, the other part I would say is dark matter, but that's a discussion for another time.
In short, no, we will not get sucked into the center. Each arm of the spiral makes one rotation every 250 million years, I beleieve.
Differential rotation is the name given to something that rotates, where the arms keep winding up. Like the blender idea. However, after a short time, say a billion years or so, the galaxy would become extremly wound up. Evidence shows that this does not happen, so differential rotation doesn't happen within galaxies.
I'm not sure if they are exactly sure how spiral arms form, but here is a good webpage to look over:
http://www.astronomynotes.com/ismnotes/s8.htm
You also have to remember that stars die out. Granted, some stars live for a vary long time. Our sun is about 6 billion years old, which means it's made 24 trips around the galactic center. There are stars that last longer than our own, and stars that burn their fuel up in a relativley short period of time. Ours is pretty much right in the middle. It will last about 12 or 13 billion years.
One could argue that the spiral arms don't wind up because many of the stars die out in their natural process.