Dark matter could be almost anything.  With little data other than how much total dark matter mass exists, we can’t decode much about what individual chunks of dark matter might be made of.  I’ve talked before about Massive Compact Halo Objects (MACHOs) and Weakly Interacting Massive Particles (WIMPs), but these are just two possibilities.  Other theorists have talked about Modified Newtonian Gravity (MNG), where gravity may work differently on the grand scale than it does on our small Earth scales.  Or perhaps it’s something I haven’t seen before.  Maybe what we call dark matter is just a large population of ancient black holes....