Photon emission from inside the innermost stable circular orbit

Abstract

We consider a situation where a light source orbiting the innermost stable circular orbit (ISCO) of the Kerr black hole is gently falling from the marginally stable orbit due to an infinitesimal perturbation. Assuming that the light source emits photons isotropically, we show that the last radius at which more than 50\% of emitted photons can escape to infinity is approximately halfway between the ISCO radius and the event horizon radius. To evaluate them, we determine emitter orbits from the vicinity of the ISCO, which are uniquely specified for each black hole spin, and identify the conditions for a photon to escape from any point on the equatorial plane of the Kerr spacetime to infinity by specifying regions in the two-dimensional photon impact parameter space completely. We further show that the proper motion of the emitter affects the photon escape probability and blueshifts the energy of emitted photons.

21 pages, 9 figures; v2: published version

References in corpus (18)

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• Photon surfaces in less symmetric spacetimes
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• Escape probability of a photon emitted near the black hole horizon
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• A Significant Feature in the General Relativistic Time Evolution of the Redshift of Photons Coming from a Star Orbiting Sgr A*
• Observability of the innermost stable circular orbit in a near-extremal Kerr black hole
• Complete classification of photon escape in the Kerr black hole spacetime
• Constraints on the dark mass distribution surrounding Sgr A*: simple ${\chi }^2$ analysis for the redshift of photons from orbiting stars

Cited by in corpus (5)

• The appearance of a merging binary black hole very close to a spinning supermassive black hole
• Photon emissions from near-horizon extremal and near-extremal Kerr equatorial emitters
• Observability of Zero-angular-momentum Sources Near Kerr Black Holes
• Photon escape in the extremal Kerr black hole spacetime
• Non-Radial Neutrino Emission upon Black Hole Formation in Core Collapse Supernovae