I have come up with what I believe maybe a unique model based on an assumption that Space-Time is actually defined by virtual particles and their decay rate. Let us, as a premise, accept it as given that virtual particles ubiquitously pop into existence in pairs and then cancel each other out everywhere in the universe.
Where there is a high density of baryonic matter the virtual particle decay rate is slow due to interference from existing particles and forces.
In deep space, between the areas of higher density, the virtual particles, meeting no interference, decay very rapidly.
This is why time itself flows more slowly near large masses.
In deep space the virtual particle decay rate is so high that the effect is mostly the release of energy. This dark energy, although infinitesimal per individual instance, is cumulative. This energy increases the distance between higher density areas where the energy is greater than the gravity between them. This allows for more virtual particles and accounts for the accelerating expansion that we see.
In areas of higher density, within galaxies for instance, the rate is slow enough that the effect is mostly additional mass for any area of higher density we measure where time is greater than 0.
This is why the outer systems of galaxies do not fly away from the galactic center of mass and rotate the galactic center of mass maintaining their relative positions. When calculating the total mass of a galaxy for any given unit of time you must count not only the observable matter but the slowly decaying virtual particles even though you cannot observe them directly.