PT2 - Theory of light propagation in gravitation fields |
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Speaker |
Patil, Mandar |
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Coauthors |
Satyabrata Sahu, D. Narasimha, Pankaj S. Joshi |
| Talk Title |
Relativistic gravitational lensing as a probe of cosmic censorship |
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Abstract |
Cosmic censorship is the one of the outstanding unsolved problem in general relativity. In this paper we study gravitational lensing in the strong field limit from the perspective of cosmic censorship to investigate whether or not naked singularities if at all they exist in nature can be distinguished from black holes. Specifically we consider both black hole and naked singularity spacetimes admitting photon spheres as well as naked singularity spacetimes without a photon sphere that were recently shown to be the end state of gravitational collapse. In the presence of the photon sphere gravitational lensing signature of naked singularities is identical to that of Schwarzschild black hole with infinitely many relativistic images and Einstein rings, all of them located beyond a certain critical angle from optic axis and the inner relativistic images all clumped together. However, in the absence of the photon sphere, which is the case for a wide range of parameter values in the naked singular spacetimes, we show that we get finitely many relativistic images and Einstein rings spaced reasonably apart from one another, some of which can be formed inside the critical angle for the corresponding Schwarzschild black hole. We also study the time delay between successive relativistic images. We show that the differential time delay between the relativistic images for naked singularities without a photon sphere progressively decreases as opposed to that for black holes and naked singularities with a photon sphere, where it is known to be roughly constant. This study suggests that the observation of relativistic images, rings and time delay would allow us to unravel the existence of the naked singularity in the absence of the photon sphere. |
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