What do the stars in the center of the Milky Way actually revolve around?
They revolve around the ‘mean gravitational field’ of the stars interior to where they are located at ant instant. The Sun orbits the Milky Way as though all the mass contributed by the tens of billions of stars inside the solar orbit is concentrated at the center of the Milky Way. Similarly, a star located 100 light years from the gravitational center of the Milky Way will feel the effects of the MILLIONS of stars inside its orbit, and a star within a few light years of the center will feel the effects of the 100s of thousands of stars inside its orbit. We thing there may also be a million solar mass black hole there too, so the mass interior to any stars orbit will include this point mass too, and not just the other stars in the nuclear star cluster.
