This make me wonder if the galactic void is full of ejected black holes which will be nearly undetectable since the X-ray radiation comes from the accretion disk and the matter falling into the black hole.
This mechanism could be potentially be another candidate for "dark matter".
This is a good observation, but gravitational lensing surveys have all but eliminated massive compact objects as a potential source of dark matter; see for example https://www.ncbi.nlm.nih.gov/pubmed/17359015.
The NIH (specifically PubMed) just indexes most scientific journals. This paper is actually in Phys. Rev. Letters (which the NIH site links to, if you click the DOI link below the abstract):
Gravitational lensing surveys coverage is pretty darn small so far it's also might not be appearant on the scales we are talking about there will need to be a pretty lucky alignment of a galaxy and a black hole given the space and relative size of both objects and the noticeable lense diameter I'm not sure that intergalactic lensing will be detectable as intragalactic ones which also are pretty rare.
Not undetectable. There is still gravity lensing. And black holes (the small ones) are still stars, or at least mass/matter that once was. That material still has a place in the equations for the evolution of stars in galaxies.
Oops, yeah that was a goof... for some reason my brain interpreted that as dark energy. I even wrote "dark matter" and didn't catch myself. Forget I even said anything ;)
