Abstract Details
| Name: Siddharth Kumar Sahoo Affiliation: National Institute of Technology, Rourkela Conference ID: ASI2025_179 Title : Imprints of Einstein-Maxwell-dilaton-axion gravity in the observed shadows of Sgr A* and M87* Authors and Co-Authors : Siddharth Kumar Sahoo, Neeraj Yadav, Indrani Banerjee Abstract Type : Poster Abstract Category : High Energy Phenomena, Fundamental Physics and Astronomy Abstract : The Kerr-Sen metric represents the exact, stationary, and axisymmetric black hole solution of Einstein-Maxwell-dilaton-axion gravity. Such a black hole is characterized by the angular momentum a acquired from the axionic field and the dilatonic charge r2 arising from string compactifications. We study the role of spin and the dilaton parameter in modifying the shape and size of the black hole critical curve, which is associated with the projection of the spherical null geodesics on the sky. We compare the theoretically derived critical curve with the Event Horizion Telescope results related to the images of M87* and Sgr A* to obtain constraints on the dilaton parameter r2. We take into account the errors in mass and distance of M87* and Sgr A* while deriving their theoretical critical curve. Our analysis reveals that the image of M87* exhibits a preference toward the Kerr scenario when the critical curve angular diameter is calculated with the central value of mass and distance. When errors in mass and distance are taken into account the allowed range of r2 turns out to be 0 ≲ r2 ≲ 1. For Sgr A*, the preferred range of r2 is 0.1 ≲ r2 ≲ 0.4 when central values of mass and distance are used to calculate the theoretical critical curve. When error bars in mass and distance are used to calculate the theoretical critical curve of Sgr A*, the preferred range of r2 turns out to be 0 ≲ r2 ≲ 0.5. Thus the image of M87* favors the Kerr scenario and allows the Kerr-Sen scenario only when errors in the mass and distance are taken into consideration while the image of Sgr A* favors the Kerr-Sen scenario and allows general relativity when errors in the mass and distance are taken into account. |