Light ring images of double photon spheres in black hole and wormhole spacetimes

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Amer Physical Soc
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The silhouette of a black hole having a critical curve (an unstable bound photon orbit) when illuminated by an optically thin accretion disk whose emission is confined to the equatorial plane shows a distinctive central brightness depression (the shadow) whose outer edge consists of a series of strongly lensed, selfsimilar rings superimposed with the disk???s direct emission. While the size and shape of the critical curve depend only on the background geometry, the pattern of bright and dark regions (including the size and depth of the shadow itself) in the image is strongly influenced by the (astro)physics of the accretion disk. This aspect makes it difficult to extract clean and clear observational discriminators between the Kerr black hole and other compact objects. In the presence of a second critical curve, however, observational differences become apparent. In this work we shall consider some spherically symmetric black hole and wormhole geometries characterized by the presence of a second critical curve, via a uniparametric family of extensions of the Schwarzschild metric. By assuming three toy models of geometrically thin accretion disks, we show the presence of additional light rings in the intermediate region between the two critical curves. The observation of such rings could represent a compelling evidence for the existence of black hole mimickers having multiple critical curves.
© 2022 American Physical Society M. G. is funded by the predoctoral Contract No. 2018-T1/TIC-10431 and acknowledges further support by the European Regional Development Fund under the Dora Plus scholarship grants. D. R. G. is funded by the Atraccion de Talento Investigador programme of the Comunidad de Madrid (Spain) No. 2018-T1/TIC-10431. D.S-C. G. is funded by the University of Valladolid (Spain), Ref. POSTDOC UVA20. This work is supported by the Spanish Grants No. FIS2017-84440-C2-1-P, No. PID2019-108485GB-I00, No. PID2020-116567GB-C21 and No. PID2020-116567GB-C21 funded by MCIN/AEI/10.13039/501100011033 ("ERDF A way of making Europe" and "PGC Generacion de Conocimiento"), the project PROMETEO/2020/079 (Generalitat Valenciana), the project H2020-MSCA-RISE-2017 Grant No. FunFiCO- 777740, the project i-COOPB20462 (CSIC), the FCT projects No. PTDC/FIS-PAR/31938/2017 and No. PTDC/FIS-OUT/29048/2017, and the Edital 006/2018 PRONEX (FAPESQ-PB/CNPQ, Brazil, Grant No. 0015/2019). This article is based upon work from COST Action CA18108, supported by COST (European Cooperation in Science and Technology). All images of this paper were obtained with our own codes implemented within Mathematica (R).
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