What is dark matter in the universe?

Decades ago, when dark matter was first proposed, it was only a product of theory, but now we know that dark matter has become an important part of the universe. The total mass of dark matter is six times that of ordinary matter, accounting for 1/4 of the energy density of the universe. More importantly, dark matter dominates the formation of the structure of the universe. The nature of dark matter is still a mystery, but if it is assumed to be a weakly interacting subatomic particle, then the large-scale structure of the universe formed from it is consistent with the observation. However, the recent analysis of the structure of galaxies and sub-galaxies shows that there is a difference between this hypothesis and the observed results, which also provides a useful place for many possible dark matter theories. These potential dark matter models can be distinguished by studying the density, distribution, evolution and environment of small-scale structures, which brings new dawn to the study of dark matter properties.