<span><span>Clouds of gas form within galaxies.
</span><span>Formation of structure within the gas clouds, due to "turbulence" and activity of new stars.
</span><span>Random turbulent processes lead to regions dense enough to collapse under their own weight, in spite of a hostile environment.
</span><span>As blob collapses, a disk forms, with growing "protostar" at the center.
</span><span>At the same time, bipolar outflows from forming star/disk system begin.
</span><span>Material is processed, moving in from the blob to the disk. What is not lost in the outflow builds up on the protostar.
</span><span>When the protostar begins to undergo fusion, it becomes a real star.
</span><span>Once the outflow ceases and the "accretion" phase that lead to the buildup of the star ends, a disk of "leftover" material is left around the star.
</span><span>At or near the end of the star-formation process, the remaining material in the "circumstellar disk" (a.k.a. "protoplanetary disk") forms a variety of planets.
</span><span>Eventually, all that is left behind is a new star, perhaps some planets, and a disk of left-over ground-up solids, visible as a "Debris Disk"around stars other than the Sun, and known as the "Zodaical Dust Disk" around the Sun.</span></span>
D: Rh- can only receive Rh-
