Galaxies

[Thrand]

What makes galaxies spin?

Why so much empty space between galaxies?

Are all galaxies as old as the "big bang?"

Do galaxies live forever?

[Woxor]

I'm taking an astronomy course right now, so I don't know precisely yet. But here's my attempt:

 

1. I don't think there's anything "making" them spin, per se, but they spin simply because they have angular momentum, and they have angular momentum simply because the constituents that formed the galaxy had it going in. I could definitely be wrong about this one, though.

 

2. Because matter tends to coalesce due to the law of gravitation (for large scales such as this). Also, since we're all rapidly moving away from the center of the universe, we end up with more and more space between galaxies simply because of geometry. (In other words, if you have finitely many galaxies on the surface of an expanding sphere, the intergalactic distance is going to increase.)

 

3. Almost. Google says the universe is 13.7 +/- 0.2 billion years old, and that the galaxy is 13.6 billion. You can easily reason that the galaxies are not quite as old, since (very) shortly after the big bang, there weren't even atoms, let alone stars, let alone galaxies. But by an astronomic scale, galaxies apparently formed pretty quickly.

 

4. Not from what I've heard. Supposedly, the universe will end with "heat death," which will be the passage into such an entropic state that everything, including galaxies, stars, planets, molecules, and perhaps even atoms will break apart and all that will be left is dust. I would imagine that the dust could still coalesce, but I don't know if you'd still call it a galaxy. But all that's just something I read somewhere, it could easily be a layman's (i.e. my) misinterpretation.

[albymangles]

not all galaxies spin, spiral galaxies like our own spin because of gravitational interactions with matter outside the galaxy while it was forming; this spin would increase as gravitation made the galaxy smaller, eventually balancing the attraction of gravity. Elliptical galaxies do not spin as they did not pick up a rotation while forming, the attraction of gravity being balanced by individual parts of the galaxy orbiting around its centre (while the galaxy has no overall rotation).

As far as your other questions galaxies are as old as the big bang in the sense that all matter was created at the big bang, this matter eventually coalesced into galaxies. Galaxy formation is undoubtably a slow process though.