T. Zannias

Universidad Michoacana de San Nicolás de Hidalgo

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U. Geppert

University of Zielona Góra

Dany Page

Universidad Nacional Autónoma de México

Olivier Sarbach

Universidad Michoacana de San Nicolás de Hidalgo

N. Montelongo García

Morelia Institute of Technology

Joaquin Estevez-Delgado

Universidad Michoacana de San Nicolás de Hidalgo

Basilis C. Xanthopoulos

University of Crete

J. Félix Salazar

De La Salle University – Dasmariñas

Kayll Lake

Queen's University

Néstor Ortiz

Universidad Nacional Autónoma de México

Israel Quirós

Universidad de Guanajuato

Cooperative Institutions

Universidad Michoacana de San Nicolás de Hidalgo

Universidad Nacional Autónoma de México

Center for Research and Advanced Studies of the National Polytechnic Institute

Instituto Politécnico Nacional

Leibniz Institute for Astrophysics Potsdam

Max Planck Society

Universidad de Guanajuato

Universidad Central "Marta Abreu" de las Villas (UCLV)

Universidad Autónoma Metropolitana

Universidad de Morelia

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Spacetimes admitting a three-parameter group of isometries and quasilocal gravitational mass

Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields (1990)

T. Zannias

Spacetimes admitting a three-parameter group of motions multiply transitive on two-dimensional spacelike orbits allow construction of a simple geometrical invariant out of the magnitudes of Killing fields, their gradients, and the metric. We show that this invariant covariantizes and geometrizes certain forms of "quasilocal mass" introduced and discussed in the literature, in particular, Misner's mass in spherical symmetry and Taub's "mass" in plane symmetry.

Plane symmetry

Circular symmetry

Mass formula

10.1103/physrevd.41.3252

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Citations (61)

Axionic charge and gravitational collapse

Physics Letters A (1990)

Basilis C. Xanthopoulos T. Zannias

Friedmann–Lemaître–Robertson–Walker metric

Initial singularity

10.1016/0375-9601(90)90085-3

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Citations (3)

Observational distinction between black holes and naked singularities: the role of the redshift function

Classical and Quantum Gravity (2015)

Néstor Ortiz Olivier Sarbach T. Zannias

We suggest that the redshift of photons traveling from past to future null infinity through a collapsing object could provide an observational signature capable of differentiating between the formation of a globally naked singularity and the formation of an event horizon. Supporting evidence for this idea is drawn from the analysis of photons with zero angular momentum through the center of a collapsing spherical dust cloud. We show that the frequency shift as a function of proper time with respect to stationary observers has distinct features depending on whether the object collapses to a black hole or a naked singularity.

Naked singularity

Black hole (networking)

10.1088/0264-9381/32/24/247001

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Citations (13)

DYNAMO ACTION ON RELATIVISTIC SPHERICAL STARS

N. Montelongo García T. Zannias

10.1142/9789812834300_0330

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General relativistic treatment of the thermal, magnetic and rotational evolution of neutron stars with crustal magnetic fields

arXiv (Cornell University) (2000)

Dany Page U. Geppert T. Zannias

We investigate the thermal, magnetic and rotational evolution of isolated neutron stars assuming that the dipolar magnetic field is confined to the crust. Our treatment, for the first time, uses a fully general relativistic formalism not only for the thermal but also for the magnetic part, and includes partial general relativistic effects in the rotational part. Due to the fact that the combined evolution depends crucially upon the compactness of the star, three different equations of state have been employed in the calculations. In the absence of general relativistic effects, while upon increasing compactness a decrease of the crust thickness takes place leading into an accelerating field decay, the inclusion of general relativistic effects intend to ``decelerate this acceleration''. As a consequence we find that within the crustal field hypothesis, a given equation of state is compatible with the observed periods $P$ and period derivative $\dot P$ provided the initial field strength and current location as well as the magnitude of the impurity content are constrained appropriately. Finally, we access the flexibility of the soft, medium and stiff classes of equations of state as candidates in describing the state of the matter in the neutron star interiors. The comparison of our model calculations with observations, together with the consideration of independent information about neutron star evolution, suggests that a not too soft equation of state describes neutron star interiors and its cooling proceeds along the `standard' scenario.

Relativistic quantum chemistry

10.48550/arxiv.astro-ph/0005301

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Citations (4)

Do supernovae make or kill pulsars

Memorie della Societa Astronomica Italiana (1998)

Dany Page U. Geppert T. Zannias

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The geometry of the tangent bundle and the relativistic kinetic theory of gases

Classical and Quantum Gravity (2014)

Olivier Sarbach T. Zannias

This paper discusses the relativistic kinetic theory for a simple collisionless gas from a geometric perspective. We start by reviewing the rich geometrical structure of the tangent bundle TM of a given spacetime manifold, including the splitting of the tangent spaces of TM into horizontal and vertical subspaces and the natural metric and symplectic structure it induces on TM. Based on these structures we introduce the Liouville vector field L and a suitable Hamiltonian function H on TM. The Liouville vector field turns out to be the Hamiltonian vector field associated to H. On the other hand, H also defines the mass shells as Lorentzian submanifolds of the tangent bundle. When restricted to these mass shells, the projection of the integral curves of L on the base manifold describes a family of future directed timelike geodesics. A simple collisionless gas is described by a distribution function on a particular mass shell, satisfying the Liouville equation. Together with the Liouville vector field the distribution function can be thought of as defining a fictitious incompressible fluid on the mass shells, with associated conserved current density. Flux integrals of this current density provide the averaged properties of the gas, while suitable fiber integrals of the distribution function define divergence-free tensor fields on the spacetime manifold such as the current density and stress–energy tensor. Finally, we discuss the relationship between symmetries of the spacetime manifold and symmetries of the distribution function. Taking advantage of the natural metric and symplectic structure on TM, we show that groups of isometries G of the spacetime manifold lift naturally to groups of isometries and symplectic flows on the tangent bundle. Motivated by these properties, we define a distribution function to be G-invariant whenever it is invariant under the lifted isometries. As a first application of our formalism we derive the most general spherically symmetric distribution function on any spherically symmetric spacetime and write the Einstein–Liouville equations as effective field equations on the two-dimensional radial manifold. As a second application we derive the most general collisionless distribution function on a Kerr black hole spacetime background.

Kinetic Theory

10.1088/0264-9381/31/8/085013

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Citations (56)

Aspects of cosmic magnetism

Revista Mexicana de Física (2007)

T. Zannias

In this paper, after a brief review of the current observational evidences regarding the phenomenon of cosmic magnetism, we discuss the problems associated ...

Magnetism

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Shadow of a naked singularity

Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D, Particles, fields, gravitation, and cosmology (2015)

Néstor Ortiz Olivier Sarbach T. Zannias

We analyze the redshift suffered by photons originating from an external source, traversing a collapsing dust cloud and finally being received by an asymptotic observer. In addition, we study the shadow that the collapsing cloud casts on the sky of the asymptotic observer. We find that the resulting redshift and properties of the shadow depend crucially on whether the final outcome of the complete gravitational collapse is a black hole or a naked singularity. In the black hole case, the shadow is due to the high redshift acquired by the photons as they approach the event horizon, implying that their energy is gradually redshifted toward zero within a few crossing times associated with the event horizon radius. In contrast to this, a naked singularity not only absorbs photons originating from the source, but it also emits infinitely redshifted photons with and without angular momenta. This emission introduces an abrupt cutoff in the frequency shift of the photons detected in directions close to the radial one, and it is responsible for the shadow masking the source in the naked singularity case. Furthermore, even though the shadow forms and begins to grow immediately after the observer crosses the Cauchy horizon, it takes many more crossing times than in the black hole case for the source to be occulted from the observer's eyes. We discuss possible implications of our results for testing the weak cosmic censorship hypothesis. Even though at late times the image of the source perceived by the observer looks the same in both cases, the dynamical formation of the shadow and the redshift images has distinct features and time scales in the black hole versus the naked singularity case. For stellar collapse, these time scales seem to be too short to be resolved with existing technology. However, our results may be relevant for the collapse of seeds leading to supermassive black holes.

Naked singularity

Observer (physics)

10.1103/physrevd.92.044035

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Citations (40)

Nonlinear instability of wormholes supported by exotic dust and a magnetic field

Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D, Particles, fields, gravitation, and cosmology (2010)

Olivier Sarbach T. Zannias

Recently, spherically symmetric, static wormholes supported by exotic dust and a radial magnetic field have been derived and argued to be stable with respect to linear radial fluctuations. In this report we point out that these wormholes are unstable due to the formation of shell-crossing singularities when the nonlinearities of the theory are taken into account.

Wormhole

10.1103/physrevd.81.047502

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Citations (13)