On the equivalence of approximate stationary axially symmetric solutions of the Einstein field equations

We study stationary axially symmetric solutions of the Einstein vacuum field equations that can be used to describe the gravitational field of astrophysical compact objects in the limiting case of slow rotation and slight deformation. We derive explicitly the exterior Sedrakyan–Chubaryan approximate solution, and express it in an analytical form, which makes it practical in the context of astrophysical applications. In the limiting case of vanishing angular momentum, the solution reduces to the well-known Schwarzschild solution in vacuum. We demonstrate that the new solution is equivalent to the exterior Hartle–Thorne solution. We establish mathematical equivalence between the Sedrakyan–Chubaryan, Fock–Abdildin and Hartle–Thorne formalisms. © 2016, Pleiades Publishing, Ltd.