What type of matter constitutes the focus of the Milky Way's 'missing mass' mystery?

Answer

Ordinary matter (protons and neutrons)

The central puzzle concerns ordinary baryonic matter—the components that form stars and planets—which was expected based on Big Bang predictions but was missing from the visible census of the galaxy.

What type of matter constitutes the focus of the Milky Way's 'missing mass' mystery?
galaxyAstronomerdark mattermassMilky Way