Ziljan:
Very nice image. But a ring cannot be that thick. Because the particles on the upper left side have to orbit to the lower right side. Then they would collide with particles orbiting in the center of the ring. Gravitation between particles of the cloud would also add to the flattening of the ring.
I guess FD has modeled the rings quite accurately.
o7
Details are important. The pic above is from an early stage in the collapse before any real structures have formed in the disk, which is demonstrated by the inner disk which is still dark and cold. Let's remember, the proto star begins its life as a roughly spherical blob of cold gas and dust. These particles are quite small! They do collide as the cloud collapses and flattens, but not very often because dust is very small and the "disk" is still mostly empty space. The collisions that do occur during the collapse are what generate the heat, slow the collapse, and increase the randomness of orbital motion of gas and dust in the disk. Eg, they do not lead immediately to nice flat ring structures
Also, the individual particles don't orbit is neat circles or ellipses at geometric angles to the plane. They interact gravitationally with dense pockets within the cloud and their vertical components are (initially) wild and unpredictable. Going in and out and up down.
If ring structures did evolve (as in the case of HL Tauri) they would not be quite so clean and orderly as ones that form tidal forces and are held in place by moons, nor quite so 2 dimensional. The disk itself would likely be a fuzzy cloud, would likely be warped or even have spiral structure from collisions with material falling perpendicular to the plane and density waves from protoplanets coalescing within the disk. Depending on the mass and materials available, there could also be a cloud of dust and icy debris that would form around the central disk obscuring it and reddening it.
In short, no two"disks" would look exactly the same. They would vary in size, shape, color, and distribution depending on the mass, history, and current evolutionary stage of the collapse.
The disk structure represents the final and unstable stage that will eventually form planets moons and asteroid belts. But to be clear, even at its most organized stage of evolution, the protoplanetary disk would be a diffuse 3-dimensional object without any sharp boundaries.
The general structure of "midlife" of a "disk" of a sun-like star would look something like this:
Not a two dimensional object, but a flaring mostly gaseous debris field surrounded by thick layers of ice and dust.
A more artistic in game rendering of the above stage of evolution might look like this:
For scale:
