Flat. Like a streak across space. Thin. Stretched out. How come whenever we see galaxies, they always look like this? NASA has the answer. And it has something to do with how a ball of dough becomes pizza.
This image of spiral galaxy ESO 373-8 was captured by NASA with the Hubble telescope. It shows a galaxy that's 25 million light years away but its shape already seems so familiar. Why is that? NASA explains:
Try spinning around in your chair with your legs and arms out. Slowly pull your legs and arms inwards, and tuck them in against your body. Notice anything? You should have started spinning faster. This effect is due to conservation of angular momentum, and it's true for galaxies, too.
This galaxy began life as a humungous ball of slowly rotating gas. Collapsing in upon itself, it spun faster and faster until, like pizza dough spinning and stretching in the air, a disc started to form. Anything that bobbed up and down through this disk was pulled back in line with this motion, creating a streamlined shape.
Angular momentum is always conserved — from a spinning galactic disk 25 million light-years away from us, to any astronomer, or astronomer-wannabe, spinning in an office chair.
Pizza. Space. Delicious.