Why do the Planets orbit their Stars? Kepler laws do not explain why the Universe is in movement. Newton’s law of Universal attraction means and needs that all celestial objects have to orbit around a gravity center: attraction force equal to centrifugal force.
Start by considering only 2 masses in the Universe, nothing else.(m1 and m2) are in equilibrium. They have a common gravity center so that (m1*r1=m2*r2) and (r1+r2=d).
Universal equilibrium means and needs Newton’s attraction force equal to the centrifugal force. Needing a centrifugal force bring the tangential velocities V1^2*m1=V2^2*m2.This why, m1 will orbit around m2 and m2 will orbit around m1.These orbits are not elliptical, but cardioidal looking spirals.Fig.1.
You may consider as many masses as you want orbiting around a common gravity center. Fig.2 shows 3 masses system and Fig 3 is for a 5 masses system.
The orbits will be spirals reaching to the common gravity center within their life-time Tmax. Now, you can consider the simple and well known physical law h=-a*t*(t-Tmax) where (a) is the (variable) gravity factor, to estimate these spirals. Fig. 4. shows the m1’s spirals for Tmax=3 cycles.
Normally there are billions of spirals. Supposing m2>m1, m2 will orbit m1 with less cycles. Anyhow the numbers of cycles depend of the approaching angles of the masses to the common gravity center. Our Sun is at the gravity center of our solar system. If any perturbation is remarked on the orbit of a planet that means a planet mass of the system is missing. On other hands the Sun orbits it’s galaxy as a total system. And this galaxy orbits another gravity center in the Universe together with the other galaxies, due to equilibrium forces. Equilibrium forces create orbital movements; billions of spiral orbits and not elliptical orbits.