The Aoa are a phenomenon that occurs when rifts for the Positive and Negative Energy Planes touch. Some planar scholars theorize that they're energy-neutral version of energons. They float along in the Astral and Ethereal planes, but can sometimes be found near planar rifts, absorbing magical energy. In fact, they do little more than float, and are only motivated into movement by the presence of strong magical auras. Which is unfortunate for people travelling through its home planes, since that requires precisely that sort of magic. If you try to attack them by magic, there's a very good chance that the spell will be reflected back on the caster.
Aoa appear in two forms: Sphere and Droplet versions. The former is the parental form, and the latter is the small blob that breaks off when it reflects enough magic.