Unstable Wormholes are wormholes created to bring aliens into sectors.
Unstable wormholes appear and disappear again during events and in the event Alien Mobilization. These alien fleets contain three Alien Hives and jam your sensors during combat, hiding ship firing arcs. The fleet itself is as fast as a rebel fleet but has a shorter pursuit time. ->More info in the page Unknown Signal Fleets
- Apparently, according to in game description. These lead to different galaxies, they cannot be traveled through however.