Multiring images of thin accretion disk of a regular naked compact object

Abstract

We discuss the importance of multiring images in the optical appearance of a horizonless spherically symmetric compact object, when illuminated by an optically thin accretion disk. Such an object corresponds to a subcase of an analytically tractable extension of the Kerr solution dubbed as the "eye of the storm" by Simpson and Visser in [J. Cosmol. Astropart. Phys. 03 ( 2022) 011], which merits in removing curvature singularities via an asymptotically Minkowski core, while harboring both a critical curve and an infinite potential barrier at the center for null geodesics. This multiring structure is induced by light rays winding several times around the object, and whose luminosity is significantly boosted as compared to the Schwarzschild solution by the modified shape of the potential. Using three toy profiles for the emission of an infinitely thin disk, truncated at its inner edge (taking its maximum value there) and having different decays with the distance, we discuss the image created by up to eight rings superimposed on top of the direct emission of the disk as its edge is moved closer to the center of the object. Our results point to the existence of multiring images with a non-negligible luminosity in shadow observations when one allows for the existence of other compact objects in the cosmic zoo beyond the Schwarzschild solution. Such multiring images could be detectable within the future projects on very long baseline interferometry.

Shadows and photon rings of regular black holes and geonic horizonless compact objects

“…The multi-ring structure is clearly visible (top figures), while the observed intensity (bottom figures) reveals that many new narrow peaks have appeared in the internal region of the impact parameter space, which are particularly visible in the GLM3 model. Indeed, the one-to-one correspondence between trajectories crossing the equatorial plane m times and the number of photon rings M is broken with M > m. This was expected on the grounds of the lessons learned from some toy-models having a potential "well" in which these new rings can be originated [82,86,87], qualitatively similar as the one found in these configurations. These new rings appear as sharp images in the optical appearance (top figures) of the object, with a strong dependence on the emission model.…”

Light Ring behind Wormhole Throat: Geodesics, Images and Shadows

“…which arise in astrophysics scenarios (see e.g. [12,29,[50][51][52][53]). We show these two functions employed for the emitted intensity in Fig.…”

Toward very large baseline interferometry observations of black hole structure

“…Naked singularities have been studied, from an imaging point of view, partially in [62], and more extensively in Refs. [26,27]. The latter paper focuses on the contribution of higher-order lensed images.…”

“…This will give us information about the experimental designs that maximize the capabilities of testing these foundational aspects. Most existing analyses in the literature have focused on specific models [26][27][28][29][30][31], while works that have attempted to keep the discussion more general using effective field theory arguments have only estimated the imprint that reflection would have on EHT images, without systematically discussing the associated image features [32]. Our work complements and extends these previous analyses, by providing a comprehensive discussion of any novel image features, as well as their observability, within a modelindependent framework in which specific models can be embedded.…”