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The equatorial motion of extended bodies in a Kerr spacetime is investigated in the framework of the Mathisson–Papapetrou–Dixon model, including the full set of effective components of the quadrupole tensor. The numerical integration of the associated equations shows the specific role of the mass and current quadrupole moment components. While most of the literature on this topic is limited to spin-induced (purely electric) quadrupole tensor, the present analysis highlights the effect of a completely general quadrupole tensor on the dynamics. The contribution of the magnetic-type components is indeed related to a number of interesting features, e.g., enhanced inward/outward spiraling behavior of the orbit and spin-flip-like effects, which may have observational counterparts. Finally, the validity limit of the Mathisson–Papapetrou–Dixon model is also discussed through explicit examples. [ABSTRACT FROM AUTHOR]

The gravitational field of a static body with the quadrupolemoment is described by an exact solution found by Erez and Rosen. Here, we investigate the role of the quadrupole in the motion, deflection and lensing of a light ray in the above metric. The standard lensing observables such as image positions and magnification have been explicitly obtained in the weak-field and smallquadrupole limit. In this limit, the spacetime metric appears as the natural generalization to quadrupole corrections of the metric form adopted also in current astrometric models. Hence, the corresponding analytical solution of the inverse ray tracing problem and the consistency with other approaches are also discussed. [ABSTRACT FROM AUTHOR]

We investigate the non-geodesic motion of a test particle inside a fluid in equilibrium, as described by the interior Schwarzschild solution, in the presence of a Poynting-Robertson-like dissipative force. The accelerated motion in the interior spacetime is (regularly) connected to the geodesic one in the corresponding external Schwarzschild background, mimicking physical conditions often occurring in spacetime regions close to stellar or compact objects. A similar analysis is repeated for the case in which the interior Schwarzschild solution is given by a Pant-Sah perfect-fluid solution. This latter case, supporting a polytropic equation of state for the interior fluid source, appears to be more appropriate for modeling situations of either stellar or cosmological interest. [ABSTRACT FROM AUTHOR]

Tidal indicators are commonly associated with the electric and magnetic parts of the Riemann tensor (and its covariant derivatives) with respect to a given family of observers in a given spacetime. Recently, observer-dependent tidal effects have been extensively investigated with respect to a variety of special observers in the equatorial plane of the Kerr spacetime. This analysis is extended here by considering a more general background solution to include the case of matter which is also endowed with an arbitrary mass quadrupole moment. Relations with curvature invariants and Bel-Robinson tensor, i.e. observer-dependent super-energy density and super-Poynting vector, are also investigated. [ABSTRACT FROM AUTHOR]

The article focuses on a study on motion of photons in the equatorial plane of Schwarzschild backgrounds of black hole which are affected by radiation drag. It informs about the calculation of the signal produced by hot spot moving in a Schwarzschild metric under the influence of a radiation field. It informs that all photons in the radiation field possess the same angular momentum and travel along metric spaces. It discusses the result which depicts astrophysical applications.

The observer-dependent tidal effects associated with the electric and magnetic parts of the Riemann tensor with respect to an arbitrary family of observers are discussed in a general spacetime in terms of certain 'tidal indicators'. The features of such indicators are then explored by specializing our considerations to the family of stationary circularly rotating observers in the equatorial plane of the Kerr spacetime. There exist a number of observer families which are special for several reasons and for each of them such indicators are evaluated. The transformation laws of tidal indicators when passing from one observer to another are also discussed, clarifying the interplay among them. Our analysis shows that no equatorial plane circularly rotating observer in theKerr spacetime can ever measure a vanishing tidal electric indicator, whereas the family of Carter's observers measures zero tidal magnetic indicator. [ABSTRACT FROM AUTHOR]