= Circular-binary orbital angular momentum
{title2=$J=\mu\sqrt{GMa}$}
For a <circular Kepler orbit>, neglecting stellar spin, the orbital <angular momentum> of a <binary star> is $J=\mu a^2\Omega=\mu\sqrt{GMa}$, where $M$ is total mass, $\mu$ is the <reduced mass>, and $a$ is separation. <Kepler's third law> also gives $J=G^{2/3}P^{1/3}M_1M_2/[(2\pi)^{1/3}M^{1/3}]$. Distances from the <center of mass> are $aM_2/M$ and $aM_1/M$; adding their individual orbital <angular momenta> proves the formula.
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