An object can spin relative to itself. Particles away from the center are constantly accelerating. Gravity or physical connection are the forces that prevent these particles from flying away.
Thinking about it, I am not even sure an object can spin relative to another object. Orbit sure, but not spin.
> An object can spin relative to itself. Particles away from the center are constantly accelerating. Gravity or physical connection are the forces that prevent these particles from flying away.
This is a reasonable description of spin for an ordinary object, but it can't be used for a black hole, because a black hole is a vacuum solution; it has no "particles". See my other post upthread for better ways to view spin for a black hole.
> I am not even sure an object can spin relative to another object. Orbit sure, but not spin.
The usual definition of "spin" makes use of the object's center of mass frame, yes. Orbital angular momentum is thus separated out.
Note, though, that strictly speaking, in relativity there is no invariant way to make this split. It works very well as an approximation for most objects (like planets and stars), but there are complications when one tries to apply it to things like black holes. That's one reason why physicists prefer other ways of defining "spinning" for black holes that don't involve any split between orbital and spin angular momentum.
An object can spin relative to itself. Particles away from the center are constantly accelerating. Gravity or physical connection are the forces that prevent these particles from flying away.
Thinking about it, I am not even sure an object can spin relative to another object. Orbit sure, but not spin.