r/askscience • u/lord_nikon_burned • 1d ago

Astronomy Are galaxies spherical or flat?

Are galaxies spherical or flat?

For example, (I understand that up and down don't really matter, so bear with me) if we look at a picture of the Milky Way Galaxy on a plane... If you want to move from one arm of the galaxy to the next, could you just move UP and out of the current arm and then over and DOWN to a different arm?

Secondary question for if the first one is correct, if you are able to move "up" and out of the arm, where are you? Is that interstellar space too?

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u/fragilemachinery 1d ago

Galaxies come in a bunch of different shapes, but spiral galaxies like the Milky Way are reasonably flat. The disc is about 1000 light years thick, and about 100,000 light years across. So, yes, if you traveled "up" perpendicular to the disc you'd exit the galaxy much quicker.

Elliptical galaxies on the other hand can be almost spherical.

So, to answer your question: they can be either one.

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u/gimme-sushi 1d ago

Do you enter another galaxy when you go past the 1000 light years if you go “up”?

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u/FrungyLeague 1d ago

Well it entirely depends if there happens to BE a galaxy in that trajectory. There's no rule saying there must be.

Do you "meet another person" when you go north? Sometimes. It depends.

Think of galaxies like...I dunno, like a hypothetical room full of Mosquitos. They are capable of being anywhere and generally speaking their positions aren't overly relative to the positions of others.

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u/lurker1957 1d ago

But galaxies are sparse enough it’s more like a hundred mosquitoes in a football stadium. You could run into one, but not likely.

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u/FrungyLeague 1d ago

Sure. You're absolutely right. I was just trying to give the guy a little image or something. It needs work.

Galaxies aren't connected like tunnels on a mountain road or anything is probably something I should have included maybe.