1,721,003 research outputs found
Concept of radius of gyration in general-relativity
No full textThe radius of gyration is a familiar concept in Newtonian mechanics and a suitably defined relativistic generalization of it turns out to be very useful for analyzing rotational effects in strong gravitational fields. The present paper contains a discussion of the properties of this quantity and of its level surfaces (the von Zeipel cylinders) and also of its connection with the effective potential for photon motion and with ideas of centrifugal force. The direction of increase of the radius of gyration gives a preferred determination of the local outward direction relevant for the dynamical effects of rotation, but this direction becomes misaligned with the global outward direction in strong-field situations. This misalignment underlies some apparently counterintuitive behavior of the centrifugal force in strong fields which has recently been the subject of considerable interest
Optical geometry for gravitational collapse and Hawking radiation
No full textThe notion of optical geometry, introduced more than 20 years ago as a formal tool in quantum field theory on a static background, has recently found several applications to the study of physical processes around compact objects. In this paper we define optical geometry for spherically symmetric gravitational collapse, with the purpose of extending the current formalism to physically interesting spacetimes which are not conformally static. The treatment is fully general but, as an example, we also discuss the special case of the Oppenheimer-Snyder model. The analysis of the late-time behavior shows a close correspondence between the structure of optical spacetime for gravitational collapse and that of flat spacetime with an accelerating boundary. Thus, optical geometry provides a natural physical interpretation for derivations of the Hawking effect based on the “moving mirror analogy.” Finally, we briefly discuss the issue of back reaction in black hole evaporation and the information paradox from the perspective of optical geometry
Optical space of the Reissner-Nordström solutions
No full textWe present an exhaustive discussion of the embedding diagrams for the optical geometry of the Reissner-Nordström solutions. Whereas in the black hole sector there are no qualitative differences with respect to the Schwarzschild case, the diagrams are considerably different if naked singularities are present. Our treatment is sufficiently general that it can be applied also to any other static spherically symmetric spacetime
Maxwell equations and the optical geometry
No full textWe show that, in conformally static spacetimes, Maxwell equations take their simplest form when written in terms of the so-called “optical metric.
Baroclinic Toroidal Figures of Equilibrium
No full textAnalytic, baroclinic solutions to Euler's equation for a rotating fluid in an external gravitational field are obtained by a nonlinear superposition of two or more barotropes. As an example, the addition of a constant angular momentum toroid to a rigid rotor barotrope is shown to generate large, thick baroclinic toroids with steep central funnels and favorable local stability properties
Curving Newtonian space
No full textWe show that the advance of the perihelion of Mercury (and other planets), as well as the deflection of light by the Sun, can be accurately calculated in Newtonian gravity, if one takes into account the fact of the curvature of space
Optical geometry analysis of the electromagnetic self-force
No full textWe present an analysis of the behavior of the electromagnetic self-force for charged particles in a conformally static spacetime, interpreting the results with the help of optical geometry. Some conditions for the vanishing of the local terms in the self-force are derived and discussed
Accretion Disks around Kerr Black Holes: Vertical Equilibrium Revisited
No full textWe re-derive the equation for vertical hydrodynamical equilibrium of stationary thin and slim accretion disks in the Kerr spacetime. All the previous derivations have been unsatisfactory, yielding unphysical singularities. Our equation is non-singular, more general, and simpler than those previously derived
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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