They could be galaxies that have been fully colonized, but searches for them have turned up nothing. Specifically: if by "fully colonized" we mean fully exploi

They could be galaxies that have been fully colonized, but searches for them have turned up nothing. Specifically: if by "fully colonized" we mean fully exploiting the energy resources of the galaxy, this would show up in the spectrum of emitted radiation, with energy being emitted as waste heat instead of starlight. Infrared surveys put the fraction of such fully colonized galaxies at less than 1 in 100,000, and consistent with none at all.