The following was written by Gastón Giribet, he is a physicist friend of mine.
After LIGO's detection of gravitational waves produced by what we understand is the coalescence of two black holes of about 30 solar masses, a (re)new idea started to gain ground: black holes with masses within the window 20 to 100 solar masses could account for a substantial portion of the dark matter cake.
Two papers on this called my attention, although as an outsider there could be much more that I miss. These papers, which appeared in March last year are https://arxiv.org/pdf/1603.00464.pdf and https://arxiv.org/pdf/1603.08338.pdf, which were eventually published in Physical Review Letters. They claim that black holes with masses around of few dozens of solar masses could be signature of dark matter. These have to be, of course, primordial black holes as we know that dark matter has been there for a long time, and therefore if we don't want to spoil what we know about early-universe cosmology, it's better these objects were already there. The idea is certainly not new as massive compact objects are one of the oldest hypothesis for dark matter nature. The remarkable thing is that, as explained to me by some colleagues these days, recently (and notably since LIGO's result) the previously-posed constraints on the population of these massive compact objects were reviewed and some people arrived to the conclusion that the accepted constraints were unjustifiably stringent and needed to be reconsidered. This opened the window to the idea that dark matter, or substantial part of it, could be made of primordial black holes of the aforementioned range of masses.
The authors of https://arxiv.org/pdf/1603.08338.pdf make the statement clear and concise: First, the LIGO's first gravitational wave event GW150914 can be explained by the coalescence of primordial black holes. Second, the expected primordial black hole merger rate would agree with the rate estimated by LIGO and Virgo collaborations if such objects constitute certain (though not all) fraction of dark matter.
I understand that this idea has also been received with skepticism by some experts, and I am hardly qualified to give an opinion. In any case, this sounds interesting to me: Is a big fraction of dark matter just a gas of a few hundred kilometers spacetime holes?
See, for instance: https://sciencetrends.com/characterizing-preferred-mass-range-primordial-black-holes-dark-matter/
