Stellar Manipulation again..

[Alneyan]

In the stock game, nebulaes are empty, except for their nebulae of course, so you won't find anything there... unless playing a custom game that has been specifically altered, of course. Removing the nebula will never create anything, but will merely uncover objects hiding within, including stars, planets...

You can build one Ringworld/Sphereworld per star in the system.