Photon emission of extremal Kerr-Newman black holes

Understand

In this paper, we deal with the null geodesics extending from the near-horizon region out to a distant observatory in an extremal Kerr-Newman black hole background.

• In particular, using the matched asymptotic expansion method, we analytically solve the null geodesics near the superradiant bound in the form of algebraic equations.
• For the case that the photon trajectories are limited in the equatorial plane, the shifts in the azimuthal angle and time are obtained.