Ok, simply a compiliation of theories:
The shivans when they shot sparky things from the front of the sathani were opening a remote portal (that is why they got so dark), and sucked part of the sun into subspace (causing the supernova) but before it went nova, the sathani used the energy in subspace to create a supertunnel that would carry them to their final destination (home planet? geneticaly encoded goal?). Maybe there was something special about capella that made it one of the few stars that could do that.
Creator of the mod that will not be coming for a while