A reverse-engineered modified-Schwarzschild solution in scalar-coupled higher-curvature gravity is presented, whose headline 'weaker singularity' claim is contradicted by its own Kretschmann-scalar results (r^-9 versus GR's r^-6).
Universal Properties of Light Rings for Stationary Axisymmetric Spacetimes
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abstract
Light rings (LRs) play an important role in gravitational wave observations and black hole photographs. In this paper, we investigate general features of LRs in stationary, axisymmetric, asymptotically flat spacetimes with or without horizons. For a nonextremal black hole, we show explicitly that there always exist at least two LRs propagating in opposite directions, where the outermost one is radially unstable. For an extremal black hole, we show that there exists at least one retrograde LR. We find that there is at least one LR which is angularly stable. The stability analysis does not involve any energy condition. Our method also applies to horizonless spacetimes and we prove that LRs always appear in pairs. Only some natural and generic assumptions are used in our proof. The results are applicable to general relativity as well as most modified theories of gravity. In contrast to previous works on this issue, we obtain much stronger results with a much more straightforward approach.
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An innovative black hole solution and thermodynamic properties in higher-order curvature gravity with a scalar field
A reverse-engineered modified-Schwarzschild solution in scalar-coupled higher-curvature gravity is presented, whose headline 'weaker singularity' claim is contradicted by its own Kretschmann-scalar results (r^-9 versus GR's r^-6).