A Proto-Planetary-Disk is a rotating disk of gas surrounding a newly born star. It is thought that material in this disk eventually clumps together (in a process known as accretion) over time to form planetary systems, or stars with orbiting planets. Proto-Planetary Discs are generally rarer than black holes, having very few in the galactic arms and even less near the Galactic Core. Proto-Planetary Disks do evolve into stars over time, with the same green flash as a new sentient race evolving, although old stars that are uninhabited may be deleted if new stars form. From space, Proto-Planetary Discs resemble red and orange black holes. Some people have tested the theory that proto-planetary disks develop into stars. A few of them claim that if a saved game is deleted, that star eventually disappears, and a proto-planetary disk becomes a new star on which to start a saved game, this system seems feasible as it would keep the number of stars in check.
There is an in-game error where you will sometimes receive the "Black Hole" item in the collection of "Galactic Objects."