Currently: Dark matter has been postulated to explain "anomal" orbital velocities of stars in galaxies. It is postulated that dark matter exists in a halo around galaxies and thus forms the correct mass which leads to the nearly constant orbital velocities.
The only relevant omnipresent particles in space are omnipresent photons (=OPs) with a small part of below 0,01 % electron pairs. These are also called omnipresent muon-neutrinos and electron-neutrinos.
Neutrinos are the only particles which meet the requirement to exist everywhere in universe, including the empty space in atoms: