We also need to discover what the dark matter is.

Based on the MACHO and LIGO results, I think stellar-mass primordial black holes are currently the best candidate. This is especially so in light of the relentless negative results for WIMPs, sparticles, sterile neutrinos and axions.

The MACHO research group estimates that it identified 100,000,000,000 massive compact objects in the Milky Way Galaxy halo, with a most typical mass of about 0.5 solar mass. The LIGO research group discovered gravitational waves from several black holes of roughly 10–30 solar mass, and their results suggest that a large population of such black holes exists.

Primordial black holes are an excellent candidate for explaining the MACHO and LIGO results. Moreover they are non-baryonic and make natural and well-motivated candidates for the enigmatic dark matter that dominates the matter content of the cosmos.

Exciting times!