Browsing by Author "Bambi, Cosimo"

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    Constraining Wormhole Geometries Using The Orbit Of S2 Star And The Event Horizon Telescope
    (2022) Jusufi, Kimet; Kumar, Saurabh; Azreg-Ainou, Mustapha; Jamil, Mubasher; Wu, Qiang; Bambi, Cosimo
    In this paper we study the possibility of having a wormhole (WH) as a candidate for the Sgr A(star) central object and test this idea by constraining their geometry using the motion of S2 star and the reconstructed shadow images. In particular, we consider three WH models, including WHs in Einstein theory, brane-world gravity, and Einstein-Dirac-Maxwell theory. To this end, we have constrained the WH throat using the motion of S2 star and shown that the flare out condition is satisfied. We also consider the accretion of infalling gas model and study the accretion rate and the intensity of the electromagnetic radiation as well as the shadow images.
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    X-ray reflection spectroscopy with Kaluza-Klein black holes
    (2020) Zhu, Jiachen; Abdikamalov, Askar B.; Ayzenberg, Dimitry; Azreg-Ainou, Mustapha; Bambi, Cosimo; Jamil, Mubasher; Nampalliwar, Sourabh; Tripathi, Ashutosh; Zhou, Menglei
    Kaluza-Klein theory is a popular alternative theory of gravity, with both non-rotating and rotating black hole solutions known. This allows for the possibility that the theory could be observationally tested. We present a model which calculates the reflection spectrum of a black hole accretion disk system, where the black hole is described by a rotating solution of the Kaluza-Klein theory. We also use this model to analyze X-ray data from the stella-mass black hole in GRS 1915+105 and provide constraints on the free parameters of the Kaluza-Klein black holes.