Why do stars and galaxies spin?

samsara15

It takes a continuous input of energy to spin, otherwise things would fly apart or stop spinning. So why do large macro objects spin, and continue to spin?

Crazy Tosser

Ever heard of angular momentum?

samsara15

Consider the following situation. A spinning globe of pure ice, say a small meteor, a meter in diameter, spinning around its own axis, approaching the sun, so that as it approaches the sun, it melts. Are you saying that the globe of ice will continue to remain a globe of water, still a meter in diameter, even after it melts?

mgb_phys

Yes and it will still spin with the same angular momentum

Vanadium 50

There's your problem right there. It doesn't. Unless an external torque is applied, once an object starts spinning, it stays spinning.