Some weapons aren't really weapons. The empire doesn't even admit that it has Excommunication technology. The fact that hundreds of systems within the empire have simply disappeared is blamed on a terrible external enemy. A ruthless, inexplicable alien force. One that justifies all of the repressive security measures that the empire practices.
Each vessel travels in stealth mode until it is in position. Once the vessels are in position, the Imperial Sovereign authorizes Excommunication from the helm of the flagship of the Battle Carrier formation. On each vessel, a device comes to life.
Excommunication Devices are reverse-engineered technology. First found by Maltruskan scientists in the Ancients' vast ruins beneath the surface of the imperial throne world of Amarna, these devices are believed to be related to the hyperspace suture technology that the Ancients used to create artificial slipknots between systems. Excommunication Devices do the reverse.
Once the devices are activated, the curvature of spacetime within the target system becomes precipitously more curved. Within a few hours, the system pinches off completely from our spacetime. The target solar system will then inhabit a starless pocket universe of its own.
An Excommunication Device is Technology +4 in Diaspora, and the Legendary +8 Tech Level in Starblazer Adventures.
Once this kind of technology becomes widespread, a civilization is at extreme risk. For that matter, even the vessels using this technology are at great risk. They will take 2 Consequences immediately upon using the weapon, due to the spacetime distortions caused by Excommunication.
Excommunication adds the - for all intents and purposes - Permanent Aspect "Pocket Universe" to a system. Its physics will be different in subtle ways from normal space. Magic may work, some kinds of technology may not work, there may be strange alien intelligences (gods, demons) within the pocket universe.
The actual duration of any Excommunication is D100 x 10,000 years. After that time, systems should in theory return to normal space.