Characterisation of circular light rays in a plasma
arXiv:2502.18831 · doi:10.1088/1361-6382/adfeb1
Abstract
It is the purpose of this paper to give a characterisation of circular light rays in a plasma on an axially symmetric and stationary spacetime. We restrict to the case of an unmagnetised, pressure-free electron-ion plasma and we assume that the plasma shares the symmetry of the spacetime. As a main tool we use two potentials, one for prograde and one for retrograde light rays, whose critical points are exactly the circular light rays in the plasma. In the case that the plasma density vanishes, the corresponding equipotential surfaces reduce to the relativistic Von Zeipel cylinders which have been discussed in many papers since the 1970s. In a plasma, the gradients of the potentials give the centrifugal and the Coriolis forces experienced by a light ray, where the plasma has an influence only on the centrifugal force. The introduction of these potentials allows us to generalise topological methods that have been successfully used for proving the existence or non-existence of circular vacuum light rays to the plasma case. The general results are illustrated with examples on Minkowski, Schwarzschild, Kerr and NUT spacetimes.
33 pages, 6 figures
References in corpus (16)
- Calculating black hole shadows: Review of analytical studies
- Shadows and strong gravitational lensing: a brief review
- Light ring stability in ultra-compact objects
- Light rings as observational evidence for event horizons: long-lived modes, ergoregions and nonlinear instabilities of ultracompact objects
- Stationary black holes and light rings
- Light propagation in a plasma on Kerr spacetime: Separation of the Hamilton-Jacobi equation and calculation of the shadow
- Gravitational lensing in a non-uniform plasma
- Gravitational lensing in spherically symmetric static spacetimes with centrifugal force reversal
- Gravitational radiospectrometer
- Physical interpretation of NUT solution
- Light rings of stationary spacetimes
- Circular motion in NUT space-time
- A Morse-theoretical analysis of gravitational lensing by a Kerr-Newman black hole
- Photon surfaces in less symmetric spacetimes
- Twisting shadows: Light rings, lensing and shadows of black holes in swirling universes
- Extremal black holes have external light rings