= Solution
On $\theta=\lambda=0$, the radial function $r\Delta=r^3+a^2r-\mu$ is strictly increasing and has the single positive root $r_+$. The curvature invariant diverges at $r=0$, and $g^{rr}=\Delta/\Sigma<0$ immediately inside the horizon, so this is a spacelike singularity. The maximally extended <Penrose diagram> therefore has the Schwarzschild form: two asymptotically flat exterior diamonds separated by future and past event horizons, with a spacelike future singularity above the black-hole regions and a spacelike past singularity below the white-hole regions. A collapse spacetime retains one exterior, the future horizon, and the future spacelike singularity.
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