A device apparently built by the Precursors to function as an artificial radiation source for cold planets. Containing an amazingly powerful exotic energy generator, the Sun Device is a relatively small apparatus that can produce 0.001 percent or so of the Sun's total radiation; this object can be placed in low orbit around a planet, meaning almost all of the radiated energy will be absorbed by the planet. This is a huge amount of energy to add to a planet at once, equivalent to giving the planet a new, artificial sun.
This apparently unique artifact was safeguarded by the Mycon for a very long time (most recently at Beta Brahe); whether it was intended for their use originally or merely found and used by them is unclear, but it was a very important tool in the Mycon's expansion, allowing them to augment the temperature of planets that would otherwise simply be too far from their stars to provide the heat the Mycon need to breed. The Mycon thus treated the Sun Device as a holy object and guarded it zealously. By using the Syreen fleet to lure most of the Mycon fleet into a trap, Captain Zelnick was able to overpower the guards at the Sun Device's world and steal it, knowing that it was the only object capable of accelerating the Process of Unification between the Chenjesu and Mmrnmhrm.