Near the end of the Fourth Hegemony, the War was going poorly for both sides. The allied races of the Seeders (as our histories have called them) were suffering greatly at the hands and claws of the A'Tarans - for whom battle has always come very easily. However, our own populations were being slowly whittled down, and eventually the leadership of the Three Clans began to realize that an end had to be made of the War, one way or another.
The decision to use Sunkiller bombs is a controversial one in the extreme - a weapon that could induce a supernova was considered the closest to a doomsday weapon as had ever existed. Both sides began to develop the technology simultaneously, in a race to see who could force the War's end by threatening the extinction of the other's homeworld.
Both our histories and those of the ancestors of modern humanity claim that the other broke the deadlock and used the weapon first - our lore says that they gave us no warning before unleashing no less than three sunkiller weapons: One in the system widely considered to be the 'front lines' of the war, one in the system where the A'Taran First Fleet was based, and the last in our own hearthsun itself. These three supernovas give the galaxy of NGC 2770 its modern name in human lore: "The Supernova Factory", ignorant of its true cause.
Texts still extant in galactic archives claim that the A'Tarans detonated these weapons themselves, either in an attempt to bring such political outrage upon their enemies as to escalate the war to a pan-galactic state, or in a horrific and suicidal 'final solution' - such that if we cannot win, no one lives.
This, of course, is nonsense. The Children of the Gods could have no possible notion of destroying themselves in such fashion. The 'evidence' given frequently points to the fact that prior to the detonations, the bulk of the A'Taran Race took to their great colony motherships and fled from the hearthworlds of the Hegemony. Why would they do this, if they did not know exactly where and when the weapons would be used?
The ultimate truth is lost to history, but it is clear enough to we loremasters that our spies must have ascertained the coming holocaust in time to warn the Elders. Knowing that we could not survive such a weapon being actually unleashed, we took what steps we could in order to assure our race's survival.
It is true that the majority of the enemy forces perished that day, leaving the races of the proto-humans decimated and setting them back uncounted generations in their development. While we too suffered grievous losses, coming near to extinction, the foresight displayed by setting out in the generation ships was enough to prevent this.
However, of the hundred ships that fled from Theta Garcellis II prior to the holocaust, many were lost in the dark years that followed. Most of the lost ships were destroyed by mishap (black holes, and other astronomical events), and others simply lost to degeneration. In part, this held true because the Elders (reeling from the obliteration of our very homesun), refused to make a permanent settlement on any planet.
The thinking was that their enemies must surely be pursuing them - it was not known at the time that the vast bulk of the enemy forces were also obliterated in the catastophe. And if the A'Tarans stopped to settle... they would be an easy target. So, on they roamed, with the Ships slowly starting to break down or become lost.
And in one particular case, lost without a trace.
For the majority of their entire history, the A'Tarans who wandered the stars have never known what happened to the Light Hope. The last transmission from it indicated that they were making a course correction due to gravitational anomaly, and they were never heard from again. The ship and the five hundred thousand aboard were believed lost to the night, and their names are still remembered.
But now, their story can finally be told. Their story continues in the thread: "The Imperial A'Tarans: Their History and The War."
As for the main pack of the A'Taran race, their story continues in the thread "The Galactic A'Tarans: Children of the Stars."