The sphere is described as small, crystalline, and completely dark. It glows with a black light as if it has an aura of blackness, a phantom light that is not light. Faintly violet. It seems to suck in the light around it.
It is said that this sphere is used to trap spren.
Could this be the spren of which Gavilar spoke (i.e., "an ancient, crucial spren) which inhabits the sphere of which Eshonai and members of the Council of Five are so afraid, which ultimately is the impetus for Gavilar's assassination?