Halo Zone
From Lexicanum
Halo Zone is the name of the region beyond the light of the Astronomican, where Imperial Navigators guiding ships during warp-jumps are no longer able to sense its guiding light and are thereby forced to navigate blindly. Doing so in the warp is extremely hazardous and most, if not all, Navigators will refuse to go beyond the borders of the Astonomican for this reason. Also, due to the difficulties in navigation, the time taken to cross a region is increased while also increasing the time differential between real- and warp-space2.
Lord Commander Solar Macharius attempted to continue his crusade into the Halo Zone, but his troops informed him that they would not go on into the unknown, possibly because they believed they would no longer be under the protection of the Emperor1.
