Sosigenes

Stellar objects that are expected to look dark are the ones that are collapsing and, according to the outside observer, will continue to do so for infinite time without actually becoming a black hole. Of course, in the early stages of collapse, a star is expected to produce observable electromagnetic radiation. As the collapse progresses, the resulting strong gravity red shifts all electromagnetic radiation to a degree that makes them unobservable. Hence, paradoxically, dark stars should not be expected to be black holes while actual primordial black holes can appear to be not dark at all.