Since matter-action gravitons are biphotons, there is not only scalar gravity due to static matter graviton shadows, but also a radiant vector gravity due to radiant matter. In other words, the radiation of stars entangles their motions with other stars and this entanglement results in radiant vector gravity.
Here is a diagram that shows scalar gravity shadows that results from the matter body bonds to the universe along with the radiant vector gravity that transfers momentum from inner to outer stars. Radiant vector gravity transfers momentum from stars inside the CofM to stars outside the CofM. This radiant momentum transfer is what keeps spiral galaxies rotating at constant velocity instead of at their Keplerian velocities.