Let be a photon in a circular orbit (r=3M). I want to know the period measured by a stationary observer at this radius.(adsbygoogle = window.adsbygoogle || []).push({});

Because we are working with a photon we cannot 'talk' about proper time, that's why I don't understand how can I calculate this.

If I had a massive particle I could do it (just finding an expression for [itex]\frac{d\phi}{d\tau}[/itex] and then calculating [itex]\Delta\tau[/itex] for [itex]\Delta\phi=2\pi[/itex].

Thanks for any help

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# Photon in a circular orbit

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