Leonardo A. Pachon, Jorge A. Rueda, Cesar A. Valenzuela-Toledo
We address the issue of the accuracy of the analytic exact solutions of the
Einstein-Maxwell equations to describe the exterior spacetime of compact stars.
As a test of accuracy, the radii of Innermost Stable Circular Orbits (ISCOs) as
given by full numerical solutions of Einstein equations and by analytic exact
exterior solutions, have been compared in the past. Here we propose an
off-equatorial test of accuracy based on the comparison of the orbital
frequencies of neutral test particles around compact objects. In particular, we
compare the Keplerian frequency, the periastron and nodal precession
frequencies, as well as the Lense-Thirring frequency, given by the Kerr
solution and and the six-parametric solution by Pachon, Rueda and Sanabria
(2006). We evidentiate the major role of high-order multipole moments, e.g. the
quadrupole and the current octupole moments, in the determination of the
orbital frequencies, especially in the rapid rotation regime. The results of
this work are relevant to cast a separatrix between Black Hole and Neutron Star
signatures.
View original:
http://arxiv.org/abs/1112.1712
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