Asia Pacific Physics Week 2024 (APPW2024)

Thursday, Nov. 7, 2024 

2:40 PM - 3:20 PM Plenary Talk: Ahmadjon Abdujabbarov (Ulugh Beg Astronomical Institute) 

Black hole shadow as a probe of gravity theories

Ahmadjon Abdujabbarov

Ulugh Beg Astronomical Institute, Tashkent, Uzbekistan

Recent observation of the supermassive black hole images of Sgr A* and M87 open a new window to develop a new test of the gravity theories. In addition, the shape of the shadow could be used to learn about extreme gravity near the event horizon and to determine which theory of gravity better describes the observations. The mathematical description of the shadow has so far used a number of simplifying assumptions that are unlikely to be met by the real observational data. We here provide a general formalism to describe the shadow as an arbitrary polar curve expressed in terms of a Legendre expansion. Our formalism does not presume any knowledge of the properties of the shadow, e.g. the location of its center, and offers a number of routes to characterize the distortions of the curve with respect to reference circles. Observations of shadows and ringdown waveforms will reveal the nature of black holes. We have also studied the motion of photons in a general parametrized metric beyond the Kerr hypothesis. We analyzed the shape of shadow with full parameters of the generally axisymmetric metric.