I'm not a computer graphics guy, but I wanna math. Theoretically, if I wanted to make the smallest possible 3d model, I would define it as four interconnected points. Each point has x, y, and z coordinates, so each model takes a theoretical minimum of 12 bytes of storage. Someone who knows computers can correct me if I'm off by a bunch.

The lower estimate is around 100,000,000,000 stars in the Milky Way. That's only 1.2 terabytes worth of my theoretical minimum 3d model. Doable! But you said all stars. The lower estimate is around 10^22 stars in the universe. That would be 120 zettabytes. That's only a few orders of magnitude off from the total available worldwide datadata storage!

Edit: I might have thought of a way to define a 3D model in just 2 bytes. You need four points that each have values for x, y, and z. They don't need 256 possible values for those, they can get by with two each. One bit can store two possible positions, so we can use as little as two bytes to define every point's position with 4 bits to spare. Behold, a tetrahedron: 0000 0100 1010 1110

Each set of four digits defines the x, y, and z coordinates for each point, as well as one extra dimension. You could use those extra four bits however you want. An extra spatial dimension, defining a color, etc. The theoretically smallest possible 3D model. Take the numbers I said up there and divide them by 6. A model for every star in the universe, and it would only take 20 zettabytes.