The "black holes as dark matter" were termed MACHOs (massive astrophysical compact halo object) https://en.wikipedia.org/wiki/Massive_compact_halo_object https:

The "black holes as dark matter" were termed MACHOs (massive astrophysical compact halo object) https://en.wikipedia.org/wiki/Massive_compact_halo_object https://en.wikipedia.org/wiki/Massive_compact_halo_object Most of that has been ruled out (see the graph on http://resonaances.blogspot.com/2016/06/black-hole-dark-matter.html http://resonaances.blogspot.com/2016/06/black-hole-dark-matt... ) and while some black holes may fall into the dark matter category, the observed "if there were that many black holes, micro lensing would be this common..." The result of those tests constrains black holes to less than 1% of the calculated dark matter... though there are some windows where there is very likely active research to try to detect black holes with those masses along with the cosmological models needed to have an early universe that produces black holes of that size in that quantity. From https://arxiv.org/pdf/2007.10722v3.pdf https://arxiv.org/pdf/2007.10722v3.pdf > Primordial Black Holes, in particular asteroid mass ones, remain a viable dark matter candidate. Further improve- ments in the theoretical calculations of the production and evolution of PBHs are required to reliably predict the abundance and properties of PBHs from a given model. Even so, it seems clear that a cosmologically interesting num- ber of PBHs can only be produced in specific models of the early Universe, and often fine-tuning is required. However, whether or not PBHs are a significant component of the DM is a question that has to be answered observationally. Novel ideas are needed here to either detect or rule out the remaining open parameter space. Note that we're dealing with really small ones that haven't evaporated yet. The chart on page 16 - with M PBH [g] and the X axis of 10^15 to 10^36 - that's grams. Also fun - https://github.com/bradkav/PBHbounds https://github.com/bradkav/PBHbounds which has them in solar masses