Discussion»Questions»Science and Technology» How's it possible that a bigger sphere could rotate around a smaller sphere in a binary relationship in space being not how it works?
They revolve around their common centre of mass, in a sort of stately pas-des-deux, because they are acting on each other.
If the two bodies are of equal mass, they both orbit a point half-way between them.
Where one body is denser than the other both will orbit an axis closer to the heavier (usually larger) one; and in time the smaller might be dragged "down" to the larger. With binary stars, the larger star can start eating the other by pulling gas from it.
If it is sufficiently larger and denser than the other, the pair's common axis is within the larger body, so that one simply spins on an eccentric axis.
Where the two bodies are sufficiently different, the orbit is very close or for all practical purposes on, the main body's own axis, like the Earth and the Sun.
My maths is weak but I think the stars are obeying an important principle called the 'Conservation of Angular Momentum', such that a small mass moving in a large radius orbit, has the same angular momentum as a large mass in a small orbit, if the two products of mass and radius are equal.