Imprints of the Janis-Newman-Winicour spacetime on observations related to shadow and accretion

Abstract

The final fate of gravitational collapse of massive stars has been a subject of interest for a long time since such a collapse may lead to black holes and naked singularities alike. Since, the formation of naked singularities is forbidden by the cosmic censorship conjecture, exploring their observational differences from black holes may be a possible avenue to search for these exotic objects. The simplest possible naked singularity spacetime emerges from the Einstein massless scalar field theory with the advantage that it smoothly translates to the Schwarzschild solution by the variation of the scalar charge. This background, known as the Janis-Newman-Winicour spacetime is the subject of interest in this work. %A further advantage of working with this spacetime is that it smoothly translates to the Schwarzschild solution by the variation of the scalar charge. We explore electromagnetic observations around this metric which involves investigating the characteristics of black hole accretion and shadow. We compute the shadow radius in this spacetime and compare it with the image of M87*, recently released by the Event Horizon Telescope Collaboration. Similarly, we derive the expression for the luminosity from the accretion disk and compare it with the observed optical luminosity of eleven Palomar Green quasars. Our analysis indicates that the shadow of M87* and the quasar optical data consistently favor the Schwarzschild background over the Janis-Newman-Winicour spacetime. The implications of this result are discussed.

arXiv comment32 pages, 4 new figures added; accepted for publication in Physical Review D

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• Superradiance evolution of black hole shadows revisited
• Einstein-Æther Gravity in the light of Event Horizon Telescope Observations of M87*
• Superradiant evolution of the shadow and photon ring of Sgr A${}^{\star }$
• Probing the Lorentz Symmetry Violation Using the First Image of Sagittarius A*: Constraints on Standard-Model Extension Coefficients
• Constraints on Barrow entropy from M87* and S2 star observations
• Thin accretion discs around spherically symmetric configurations with nonlinear scalar fields
• Testing Born-Infeld $f(T)$ teleparallel gravity through Sgr A${}^{\star }$ observations
• Echoes from a singularity
• Revisiting timelike geodesics in the Fisher-Janis-Newman-Winicour-Wyman spacetime
• Imaging ultra-compact objects with radiatively inefficient accretion flows
• Singularities in static spherically symmetric configurations of General Relativity with strongly nonlinear scalar fields
• Triple path to the exponential metric
• Relativistic time delay analysis of pulsar signals near ultra-compact objects
• Shadows in conformally related gravity theories
• Analogue metric in a black bounce background
• Gravitational Black Hole Shadow Spectroscopy
• Nonspherically-symmetric black hole in Einstein-massless scalar theory
• Redshift Spectroscopy as a Probe of Regular Black Holes, Black Bounces, and Scalar-Hair Compact Objects
• Orbital Motion in Spacetimes Influenced by the Presence of Scalar and Electromagnetic Fields
• Supergravity $p$-branes with scalar charge
• Photon Ring Dimming as a Signature of Photon-Axion Conversion in Janis-Newman-Winicour Naked Singularity