The Skeleton Nebula is a nebula.

Fiction

Cybertron cartoon

Located about five thousand light years away from Cybertron, the Skeleton Nebula boasted dark and gaseous clouds. After recovering the Planet Map, Vector Prime, Scattorshot and Red Alert found that the space/time tunnel to Gigantion existed within the Skeleton Nebula. After securing the Ogygia for use as a transport, the Autobots set out for the tunnel only to be attacked by the Atlantis shortly after entering. Warp

Animated cartoon

The Skeleton Nebula was a region of space in the Milky Way. It contained Gigantion and the destroyed Planet X. The AllSpark Almanac II

Ask Vector Prime

In Viron 102.0 Beta, the Elite Guard blockaded Planet X in the Skeleton Nebula. Ask Vector Prime, 2015/09/22