Publication: Shadows of boson and Proca stars with thin accretion disks
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2022-10-07
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Amer Physical Soc
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Abstract
In this work, we obtain the shadow images of spherically symmetric scalar boson and Proca stars using analytical fittings of numerical solutions, when illuminated by a geometrically thin accretion disk. We chose a sample of four boson and four Proca stars with radii ranging from more compact configurations with R '' 9M to more dilute configurations with R '' 20M, where M is the total mass of the bosonic star. In these configurations, the absence of the light sphere (the locus of unstable bound geodesics) makes the optical appearance of these stars to be dominated by a single luminous ring enclosing a central brightness depression, and no further photon rings are available. We show that if one considers face-on observations and a disk model whose emission is truncated at some finite radius at which the luminosity attains its maximum value, both the size of the shadow, as well as the luminosity and depth of the bright region, are heavily influenced by the emission profile, with the choice of the type and parameters of the bosonic stars in our samples having a sub-dominant influence. These differences are nonetheless significantly magnified when one allows the accretion disk to extend close enough to the center of the star. Our results point out that even though bosonic stars are horizonless and do not have a photon sphere, some of them may be able to produce conventional black hole shadowlike images provided that their compactness is large enough, thus being potentially consistent with current and future observations.
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J. L. R. is supported by the European Regional Development Fund and the program Mobilitas Pluss (MOBJD647), and thanks the Department of Theoretical Physics at the Complutense University of Madrid for their hospitality during the elaboration of this work. D. R. G. is funded by the Atraccion de Talento Investigador program of the Comunidad de Madrid (Spain) No. 2018-T1/TIC-10431, and acknowledges fur-ther support from the Ministerio de Ciencia, Innovacion y Universidades (Spain) Project No. PID2019-108485 GB-I00/AEI/10.13039/501100011033 ("PGC Generacion de Conocimiento") and the FCT projects No. PTDC/FIS-PAR/31938/2017 and No. PTDC/FIS-OUT/29048/2017. This work is also supported by the Project No. PROMETEO/2020/079 (Generalitat Valenciana), and the Edital 006/2018 PRONEX (FAPESQ-PB/CNPQ, Brazil, Grant 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).