Browsing by Author "Quevedo H."

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C 3 matching for asymptotically flat spacetimes
(Institute of Physics Publishing, 2019) Gutiérrez-Piñeres A.C.; Quevedo H.
We propose a criterion for finding the minimum distance at which an interior solution of Einstein's equations can be matched with an exterior asymptotically flat solution. The location of the matching hypersurface is thus constrained by a criterion defined in terms of the eigenvalues of the Riemann curvature tensor by using repulsive gravity effects. To determine the location of the matching hypersurface, we use the first derivatives of the curvature eigenvalues, implying C 3 differentiability conditions. The matching itself is performed by demanding continuity of the curvature eigenvalues across the matching surface. We apply the C 3 matching approach to spherically symmetric perfect fluid spacetimes and obtain the physically meaningful condition that density and pressure should vanish on the matching surface. Several perfect fluid solutions in Newton and Einstein gravity are tested. © 2019 IOP Publishing Ltd.
Conformastatic disk-haloes in Einstein-Maxwell gravity
(2013) Gutiérrez-Piñeres A.C.; González G.A.; Quevedo H.
We present a relativistic model describing a thin disk surrounded by a halo in the presence of an electromagnetic field. The model is obtained by solving the Einstein-Maxwell equations on a particular conformastatic spacetime background and by using the distributional approach for the energy-momentum tensor. A class of solutions is obtained in which the gravitational and electromagnetic potentials are completely determined by a harmonic function only. A particular solution is given that is asymptotically flat and singularity free, and satisfies all the energy conditions. © 2013 American Physical Society.
Motion of test particles in the field of a naked singularity
(American Physical Society, 2016) Boshkayev K.; Gasperín E.; Gutiérrez-Piñeres A.C.; Quevedo H.; Toktarbay S.
We investigate the motion of test particles in the gravitational field of a static naked singularity generated by a mass distribution with a quadrupole moment. We use the quadrupole metric (q metric) which is the simplest generalization of the Schwarzschild metric with a quadrupole parameter. We study the influence of the quadrupole on the motion of massive test particles and photons and show that the behavior of the geodesics can drastically depend on the values of the quadrupole parameter. In particular, we prove explicitly that the perihelion distance depends on the value of the quadrupole. Moreover, we show that an accretion disk on the equatorial plane of the quadrupole source can be either continuous or discrete, depending on the value of the quadrupole. The inner radius of the disk can be used in certain cases to determine the value of the quadrupole parameter. The case of a discrete accretion is interpreted as due to the presence of repulsive gravity generated by the naked singularity. Radial geodesics are also investigated and compared with the Schwarzschild counterparts. © 2016 American Physical Society.
Newman–Janis Ansatz in conformastatic spacetimes
(Springer New York LLC, 2016) Gutiérrez-Piñeres A.C.; Quevedo H.
The Newman–Janis Ansatz was used first to obtain the stationary Kerr metric from the static Schwarzschild metric. Many works have been devoted to investigate the physical significance of this Ansatz, but no definite answer has been given so far. We show that this Ansatz can be applied in general to conformastatic vacuum metrics, and leads to stationary generalizations which, however, do not preserve the conformal symmetry. We investigate also the particular case when the seed solution is given by the Schwarzschild spacetime and show that the resulting rotating configuration does not correspond to a vacuum solution, even in the limiting case of slow rotation. In fact, it describes in general a relativistic fluid with anisotropic pressure and heat flux. This implies that the Newman–Janis Ansatz strongly depends on the choice of representation for the seed solution. We interpret this result as a further indication of its applicability limitations. © 2016, Springer Science+Business Media New York.
Test particles in a magnetized conformastatic spacetime
(American Physical Society, 2016) Gutiérrez-Piñeres A.C.; Capistrano A.J.S.; Quevedo H.
A class of exact conformastatic solutions of the Einstein-Maxwell field equations is presented in which the gravitational and electromagnetic potentials are completely determined by a harmonic function. We derive the equations of motion for neutral and charged particles in a spacetime background characterized by this class of solutions. As an example, we focus on the analysis of a particular harmonic function, which generates a singularity-free and asymptotically flat spacetime that describes the gravitational field of a punctual mass endowed with a magnetic field. In this particular case, we investigate the main physical properties of equatorial circular orbits. We show that due to the electromagnetic interaction, it is possible to have charged test particles which stay at rest with respect to a static observer located at infinity. Additionally, we obtain an analytic expression for the perihelion advance of test particles and the corresponding explicit value in the case of a punctual magnetic mass. We show that the analytical expressions obtained from our analysis are sufficient for being confronted with observations in order to establish whether such objects can exist in nature. © 2016 American Physical Society.
Variational thermodynamics of relativistic thin disks
(Springer New York LLC, 2015) Gutiérrez-Piñeres A.C.; Lopez-Monsalvo C.S.; Quevedo H.
We present a relativistic model describing a thin disk system composed of two fluids. The system is surrounded by a halo in the presence of a non-trivial electromagnetic field. We show that the model is compatible with the variational multifluid thermodynamics formalism, allowing us to determine all the thermodynamic variables associated with the matter content of the disk. The asymptotic behavior of these quantities indicates that the single fluid interpretation should be abandoned in favor of a two-fluid model. © 2015, Springer Science+Business Media New York.