UltraTech LEEC species

[iancampbell]

It's worth noting that the civilisation mentioned doesn't have to look like empty space; it only has to mimic a normal star in terms of its emission spectrum and so on. A Dyson swarm programmed to emit radiation mimicking a red giant (complete with starspots and so on) would probably look much like such a star from a distance and therefore escape notice that way. Camouflage rather than invisibility.