Somewhere in the Galaxy, a star in a triple-star system went supernova. The singularity which formed began feeding on it's partners, devouring them and adding their mass to its own. Quantum physics now take over; without going into too much detail, suffice it to say that something like a wormhole, a "poke," or "rip," has opened up between space and time and dimensions. This weirdness exists between the Intergalactic space through which the Vong are passing, "our" Galaxy, and the Darker Realms (read here another dimension.)

The supernova would not have been yet seen, other than by systems close enough for the light of it to reach them so quickly. Those systems would of course, be destroyed. BUT the openings are instantaneous. We do not have to see the supernova to recognize the reality of the wormholes/rips/tears. They are there, while light tootles along dragging the message of the great explosion along with it.

SO, no references to the supernova, please!

In keeping with our reality, the imps are sill in the Darker Realms -- where a wormhole has now been opened. But since all supernatural/supranatural powers have been temporarily blocked by That Which Is, these imps now cannot change form to cope with our reality.