Omicron Delta/Kappa starspheres

[Enkidu]

There's two explanations I've heard.

The first? Science. Star systems actually travel at great velocity through space. During the formation of the star system, the stars would have drawn mass from the surrounding nebula and made a functional clearing. Since star systems move (and not necessarily at the same velocity as the nebula surrounding them), it's entirely possible that the system could clear a tunnel through a bizarrely dense nebula like the edge nebula is. You can see the Omega nebula at the end of the Kappa tunnel.

The second is that both systems are the work of intelligent K'vosh design and that they were effectively dropped into place out of hyperspace, transporting the pre-existing matter out of the local space to some other part of the universe. The K'vosh have illustrated abilities to cross spacetime and dimensions without functional limits. In the case of Delta, Delta is surrounded by dark matter fields (which means it's a good thing too the area is cleared, as nothing would survive there), whilst Kappa is surrounded by a particularly dense region of the edge nebula and physically bisects the nebula from one side to the other. Since Kappa is very, very old, the edge nebula encroaching into the reachable area of the system is a sign that the tunnel's shape is starting to decay as the nebula moves on an independent velocity vector. In a few million years, Kappa would be filled by the edge nebula.

The second explanation is fortified by the presence of K'vosh active intelligence under the service of Gammu which lead to the uplift to sentience of human polymorphic VI left on the planet by the initial colonists.