Basically, there are 2 hypothesis: WIMPs and MACHOs.
WIMPs stands for Weakly Interacting Massive Particles, and proposes that DM consist of yet unknown massive particles that don’t interact much with regular matter. The problem with that hypothesis is that no such particles are predicted by Standard Model and decades of searching for any traces of those particles didn’t yield anything.
MACHOs stands for Massive Compact Halo Objects and assumes that DM in galactic halos consists of some known dark objects, most likely Black Holes. The question is: where those black holes come from. There is a model of cyclical universe by Gorkavyi, Mathers et al, where those are primordial black holes left from the previous cycles of the universe. It also explains galaxy formation in early universe (observed by JWST) and predicted gravitational wave background recently discovered by NANOGrav.
WIMPs stands for Weakly Interacting Massive Particles, and proposes that DM consist of yet unknown massive particles that don’t interact much with regular matter. The problem with that hypothesis is that no such particles are predicted by Standard Model and decades of searching for any traces of those particles didn’t yield anything.
MACHOs stands for Massive Compact Halo Objects and assumes that DM in galactic halos consists of some known dark objects, most likely Black Holes. The question is: where those black holes come from. There is a model of cyclical universe by Gorkavyi, Mathers et al, where those are primordial black holes left from the previous cycles of the universe. It also explains galaxy formation in early universe (observed by JWST) and predicted gravitational wave background recently discovered by NANOGrav.