>aren't most galaxies disc shaped?

Uhmm... "yes and no". Most galaxies are disk shaped, but most stars in the universe are in elliptical galaxies, which are "blob-shaped". Elliptical galaxies are really huge, so a relatively small number of them really dominate. For example, the relatively nearby M87 is 200x the mass of the Milky Way.

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>Not very hard to imagine that since gravity is the force that rules over galaxies, solar systems and planets, then the distribution of stars around the massive object in the galaxy, the distribution of planets around a star, and the rings around a planet, is all from the same force,

Uhmm... "yes and no". Gravity is king, but there is also gas pressure.

This happens to be my area of research, so I hope you won't mind if I take a tangent:

In a pure N-body system with no gas, the long-term evolution is that close encounters between massive particles (e.g. planets, stars) cause random perturbations to the orbits, so over the the system approaches the shape of a blob. You can see this in globular clusters inside the Milky Way, and you see it in elliptical galaxies.

The reason disk galaxies and planetary systems don't look like that is that they were originally made from a gas cloud. In a gas cloud, gas particles collide with each other, and that tends to remove the random motions. So you are left with only the average motion, corresponding to the "net" angular momentum of the system. And that's how you get those clean, flat disks. The disk around a black hole is the same.

Gravity Only = Blob

Gravity + Gas = Disk

Today the solar system has almost no gas, and the Milky Way has already used up 99% of its gas. But because the planets and the stars were born in the gas, their present orbits reflect the shape of that gas. But if you look within the Milky Way, you will see that the oldest stars have more random orbits, making a thicker disk than the one made by the youngest stars. These are in fact called the thick disk and the thin disk.

Oh, and I just thought of another example. The galactic bulge of the Milky Way has a very large star density and it is very old, and that's why it looks like a blob. It's like a mini elliptical galaxy.

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>Maybe if the massive thing at the middle wasn't rotating it wouldn't spread out into a disc, i'm no astrophysician.

I mean this in the kindest possible way: The term is "astrophysicist".

A physician is a type of doctor (what can I say? English makes no sense).

A physicist is a scientist that studies physics.