Now I can't help but wonder if some of the classic Dr. Who--and even the newer ones--still mistake galaxy for star system. In Genesis of the Daleks, we hear about seven galaxies. I think that was star systems.
Unlikely. Surely Skaronian knowledge of astronomy would not be limited to a mere seven star systems. And the statement about there being no life in "the seven galaxies" besides their own could work if they were in a cluster of seven dwarf elliptical galaxies, say. That type of galaxy doesn't have much new star formation and thus wouldn't be as likely to have a lot of the heavy elements necessary to form planets that might potentially support life.
Although, of course, Doctor Who
is fantasy, so real astrophysics principles don't matter much one way or the other.