...$\alpha $[*]
The equilibrium orbit is circular with radius a0, so that $h_0=m a_0^2 \omega_0$ and, since it is co-rotating with the black hole, $\omega_0=\omega_{\rm Kerr}$. With respect to the moment of inertia of the black hole $m_1 r_{\rm (1)g}^2 R_1^2=J_{\rm bh}/\omega_{\rm
Kerr}$, the moment of inertia of the asteroid can be neglected. According to Ashtekar & Krishnan (2004), $J_{\rm bh}/\omega_{\rm Kerr}=M_{\rm
bh}R_{\rm h}^2$, where $R_{\rm h}$ is the horizon radius of the black hole, which becomes $2~r_{\rm g}$ in the limit of small $a_{\rm
Kerr}$.
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... equation[*]
The exchange $\alpha \rightarrow \alpha^\prime$ changes the unstable equilibrium state  $\tilde r_-$ to the attractor $\tilde r_{\rm p}=1$and vice versa with respect to the tracks shown in Hut (1982).
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...$\alpha^\prime=9720$)[*]
This is an unreasonably large number with respect to our problem, but sufficiently small and convenient to show the topology of the solution space.
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...Hut (1981)[*]
For the sake of simplicity we neglect the contribution of work done by the tangential component of tidal force, which depends on the difference between the orbital and spin period.
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Copyright ESO 2008