Given that the nature of a surface is given by the sign of g(adsbygoogle = window.adsbygoogle || []).push({}); ^{(i)(i)}and for the Boyer-Lindquist form of the Kerr solution g^{11}= -Δ/ρ^{2}, then surely any surface of constant r where r > r_{+}will have a negative value for g^{11}, so how can S_{+}be timelike?

Also on page 259, just below equation (19.70), he says "These curves are not geodesics, but are the world-lines of photons initially constrained to orbit with fixed r and θ. " How do you constrain photons?

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# D'Inverno Problem 19.10 Stationary Limit

Can you offer guidance or do you also need help?

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