rotation around center of mass

Hey all!
I always use this principle when I do exercises, but today I found out, that I can't explain why it's valid. What I'm talking about is that when you apply a torque to a free object it will always start to rotate around it's center of mass rather than just an arbitrary point. Why is that? I know that rotation around the cm requires the least energy so if there was some fundamental theorem saying that a system always tends towards the least increase in energy or whatever, that might explain it.
Yet I don't think that's the way to go, so can someone explain it please?
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 Recognitions: Homework Help I never really questioned it myself but I think it has to do with rotation about the center of mass being the most stable position. Otherwise rotating about another axis (which is not the center of mass) usually causes high instability. An example is rotating unbalance.