30 research outputs found
The influence of the Lande -factor in the classical general relativistic description of atomic and subatomic systems
We study the electromagnetic and gravitational fields of the proton and
electron in terms of the Einstenian gravity via the introduction of an
arbitrary Lande -factor in the Kerr-Newman solution. We show that at length
scales of the order of the reduced Compton wavelength, corrections from
different values of the -factor are not negligible and discuss the presence
of general relativistic effects in highly ionized heavy atoms. On the other
hand, since at the Compton-wavelength scale the gravitational field becomes
spin dominated rather than mass dominated, we also point out the necessity of
including angular momentum as a source of corrections to Newtonian gravity in
the quantum description of gravity at this scale.Comment: 11 pages, 2 figure
Chaotic dynamics around astrophysical objects with nonisotropic stresses
The existence of chaotic behavior for the geodesics of the test particles
orbiting compact objects is a subject of much current research. Some years ago,
Gu\'eron and Letelier [Phys. Rev. E \textbf{66}, 046611 (2002)] reported the
existence of chaotic behavior for the geodesics of the test particles orbiting
compact objects like black holes induced by specific values of the quadrupolar
deformation of the source using as models the Erez--Rosen solution and the Kerr
black hole deformed by an internal multipole term. In this work, we are
interesting in the study of the dynamic behavior of geodesics around
astrophysical objects with intrinsic quadrupolar deformation or nonisotropic
stresses, which induces nonvanishing quadrupolar deformation for the
nonrotating limit. For our purpose, we use the Tomimatsu-Sato spacetime [Phys.
Rev. Lett. \textbf{29} 1344 (1972)] and its arbitrary deformed generalization
obtained as the particular vacuum case of the five parametric solution of Manko
et al [Phys. Rev. D 62, 044048 (2000)], characterizing the geodesic dynamics
throughout the Poincar\'e sections method. In contrast to the results by
Gu\'eron and Letelier we find chaotic motion for oblate deformations instead of
prolate deformations. It opens the possibility that the particles forming the
accretion disk around a large variety of different astrophysical bodies
(nonprolate, e.g., neutron stars) could exhibit chaotic dynamics. We also
conjecture that the existence of an arbitrary deformation parameter is
necessary for the existence of chaotic dynamics.Comment: 7 pages, 5 figure
On the relativistic precession and oscillation frequencies of test particles around rapidly rotating compact stars
Whether analytic exact vacuum(electrovacuum) solutions of the
Einstein(Einstein-Maxwell) field equations can accurately describe or not the
exterior spacetime of compact stars remains still an interesting open question
in Relativistic Astrophysics. As an attempt to establish their level of
accuracy, the radii of the Innermost Stable Circular Orbits (ISCOs) of test
particles given by analytic exterior spacetime geometries have been compared
with the ones given by numerical solutions for neutron stars (NSs) obeying a
realistic equation of state (EoS). It has been so shown that the six-parametric
solution of Pach\'on, Rueda, and Sanabria (2006) (hereafter PRS) is more
accurate to describe the NS ISCO radii than other analytic models. We propose
here an additional test of accuracy for analytic exterior geometries based on
the comparison of orbital frequencies of neutral test particles. We compute the
Keplerian, frame-dragging, as well as the precession and oscillation
frequencies of the radial and vertical motions of neutral test particles for
the Kerr and PRS geometries; then we compare them with the numerical values
obtained by Morsink and Stella (1999) for realistic NSs. We identify the role
of high-order multipole moments such as the mass quadrupole and current
octupole 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 (BH) and NS signatures as well as probe the
nuclear matter EoS and NS parameters from the Quasi-Periodic Oscillations
(QPOs) observed in Low Mass X-Ray Binaries.Comment: 14 pages, 10 figure
Realistic Exact Solution for the Exterior Field of a Rotating Neutron Star
A new six-parametric, axisymmetric and asymptotically flat exact solution of
Einstein-Maxwell field equations having reflection symmetry is presented. It
has arbitrary physical parameters of mass, angular momentum, mass--quadrupole
moment, current octupole moment, electric charge and magnetic dipole, so it can
represent the exterior field of a rotating, deformed, magnetized and charged
object; some properties of the closed-form analytic solution such as its
multipolar structure, electromagnetic fields and singularities are also
presented. In the vacuum case, this analytic solution is matched to some
numerical interior solutions representing neutron stars, calculated by Berti &
Stergioulas (Mon. Not. Roy. Astron. Soc. 350, 1416 (2004)), imposing that the
multipole moments be the same. As an independent test of accuracy of the
solution to describe exterior fields of neutron stars, we present an extensive
comparison of the radii of innermost stable circular orbits (ISCOs) obtained
from Berti & Stergioulas numerical solutions, Kerr solution (Phys. Rev. Lett.
11, 237 (1963)), Hartle & Thorne solution (Ap. J. 153, 807, (1968)), an
analytic series expansion derived by Shibata & Sasaki (Phys. Rev. D. 58 104011
(1998)) and, our exact solution. We found that radii of ISCOs from our solution
fits better than others with realistic numerical interior solutions.Comment: 13 pages, 13 figures, LaTeX documen
Caracterizaci贸n biol贸gica de Paz de Ariporo. Identificaci贸n de especies claves para establecer l铆mites de humedales.
Se exponen los resultados y evaluaciones en campo de la ventana piloto de humedales de Paz de Ariporo- Hato Corozal en el marco del convenio 005 (13-014) entre el Instituto Humboldt y el Fondo Adaptaci贸n.Bogot谩Subdirecci贸n de Servicios Cient铆ficos y Proyectos Especiale