SPOLER AHEAD! DO NOT CONTINUE BEFORE YOU HAVE COMPLETED THE CAMPAIGN OR ARE VERY VERY VERY SURE THAT YOU WANT TO KNOW HOW THE CAMPAIGN ENDS!!!!!
At endprt2a.avi, Admiral Petrach says that (possibly) the Shivans destroyed the capella star to form a bridge between our galaxy, and their own.
What if the ancients somehow obliberated a former passage, sealing of a lot of Shivans from their homeworld. The Shivans off-course didn't like that, and (being very agressive) started blowing the ancients to very tiny bits. The Ancients didnt suspect this and were being completely overrun. The Shivans then searched the entire galaxy for a way back home, obliberating anything non-shivan thing they find, for they think it is ancient.
They came closer to a place where they could find a way home. However, after the attack at Ros 128, they encountered fierce resistance. These descendants were adapting and fighting back, again preventing them to reach their homeworlds. So, they tried to wipe them out, locating the homeworlds of these descendants and killing all live on it (vengeance). they faced another shock when one of their main ships, the krkrkrkr k klick r krr ktkrrk (terrans call it the SD Lucifer) was destroyed by a few fighters. They called of their attacks and waited for the whole exodus fleet to come, since on of the systems of those descendants could be a key to their way home.
**32 years later**
The shivans were suprised that a terran ship was actually heading into territory previously hidden. That these descendants could find those things ment that they're mabye surviving ancients in those outer systems. The KRRKLRLKRRRRR (SD Ravana) was destroyed a few days later, and the Ancients' descendants started moving into the nabulea
The Shivans knew that they had to either find a way home, or nullify the threat completely.
They sent in one of their jaggernauts, and let her head for the capella star. In krrrrrrrrrrrst (Gamma Draconis) KRKRRKKKKRRRR (Terran Double-Ace and Lieutenant Junior Grade Joshua (promoted to lieutenant after that mission, and now Triple-Ace) destroyed the 4 forward beam cannons of the Sathanas, the Jaggernaut didn't need those things, as long they could open a way to the homeworld of the shivans everything would be fine. The shivans didn't count on the colussus however, and where oblibirated.
Then, desperate to find a way home, the shivans send their whole fleet in, and the terrans and vesudans retreated to their other systems, and managed to obliberate a jumphole to their way home.
At the endgame, the shivan jaggernauts activated their special weapon (a time accalerator?) and let the capella star change into a supernova.
No one can knows wat happened after then, but, a large supernova eventually becomes an black hole (in theory) and (in theory) 2 black holes form a wormhole, wich allows someone to cover enermous distance's... from one galaxy, to another.
Terran Lieutenant Joshua.