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The purpose of this note is to investigate the geodesic motion in the gravitational field of a rotating source, making use of the exact empty-space solutions of Einstein’s equations given by Kerr. The earlier weak-field approximate solutions of Lense and Thirring for a rotating body are also examined to compare them with the exact case and with the Schwarzschild nonrotating one, whose geodesic properties are also briefly summarized. The behaviour of single orbits, for example the precession of the pericenter, will not be mentioned since they have been extensively analysed in the cited references. The differential equations of the geodesics are analysed from an analytical point of view in order to recognize the shape of the loci of the turning points for the test particles without introducing numerical values of the parameters involved such asa (specific angular momentum of the rotating body) andΓ (test particle’s effective energy). Diagrams are given which show the behaviour of the geodesics for different ranges of these parameters. An attempt to make a physical comparison between these three cases has been done in the last Section.

The purpose of this note is to describe a relativistic effect of energy accumulation which arises when spherically symmetric configurations are enclosed in a sufficiently small volume. Conditions for a release of this energy are analysed and possible physical applications of this effect are suggested.

The effective potential of the equatorial circular geodesics in Kerr metric show a sharp discontinuity from positive to negative values, when a→m. It is shown that when a is in the small range 1.088 m > a > m, stable circular orbits exist with negative energy (with respect to infinity); this implies that, if accretion takes place, a Kerr naked singularity is slowed down. The efficiency of this process increases as a→m. Therefore, in the above range of a, Kerr naked singularities should decay to a black-hole state.

It is shown that if a space-time has an isometry group whose Killing vector is time-like in a region V and if there exists one closed time-like curve somewhere in the space-time, then under suitable conditions on V (including the absence of horizons) there is a closed time-like curve through every point of the space-time.

We find the total effective gravitational mass which acts on a particle moving in the Kerr–Newman metric. We also identify the contribution to that mass by the electric field energy which is stored in any given portion of the space surrounding the metric source.

The motion is analysed, in general, in the Kerr metric with the use of first integrals. Some of the high-energy particles and photons are found to move in a giant vortex around the axis of symmetry above and below the equatorial plane, dragged by the gravitational field.

This study aimed 1) to assess whether patients with an exaggerated blood pressure response to the doctor's presence ("white coat" effect) also display a pattern of enhanced blood pressure reactivity to mental stress and physical exercise and 2) to determine the presence of left ventricular structural and filling abnormalities in patients with white coat hypertension. We studied 56 (40 men) consecutive patients (mean [SD] age, 46.4 [9.1] years) whose clinic blood pressure was repeatedly high. Patients were classified as having white coat hypertension (n = 20) if both their mean daytime (from 7 AM to 11 PM) ambulatory systolic and diastolic blood pressures were less than 134 and 90 mm Hg, respectively. Patients were considered to have persistent hypertension (n = 36) if daytime systolic blood pressure was 134 mm Hg or more or diastolic blood pressure was 90 mm Hg or more. Eighteen subjects with clinic blood pressure lower than 140/90 mm Hg served as a normotensive control group. Blood pressure reactivity from baseline to mental arithmetic, isometric handgrip, and cycle ergometry did not display any difference among the three groups. The white coat hypertensive group had left ventricular mass index lower than the persistent hypertensive group but higher than the normotensive group. Doppler indexes of left ventricular diastolic filling displayed similar abnormalities in the white coat and persistent hypertensive groups compared with the normotensive group.(ABSTRACT TRUNCATED AT 250 WORDS)

We present N-body simulations of the collapse of six triaxial systems having the angular momentum aligned with one of their principal axes. Two different initial density distributions are chosen. The final relaxed states of the simulations show (1) a net outflow of angular momentum from the inner regions to the outer halo, consistent with the loss expected during the formation of elliptical galaxies; (2) a general misalignment of the average spin of the internal mass fractions with respect to that of the total system. Finally, some considerations are given concerning the occurrence of the necessary condition for the formation of a black hole at the center of these systems

We propose a simple and unambiguous way to deduce the parameters of black holes which may reside in AGNs and some types of X-ray binaries. The black-hole mass and angular momentum are determined in physical units. The method is applicable to the sources with periodic components of variability, provided one can assume the following: (i) Variability is due to a star or a stellar-mass compact object orbiting the central black hole and passing periodically through an equatorial accretion disk (variability time-scale is given by the orbital period). (ii) The star orbits almost freely, deviation of its trajectory due to passages through the disk being very weak (secular); the effect of the star on the disk, on the other hand, is strong enough to yield observable photometric and spectroscopic features. (iii) The gravitational field within the nucleus is that of the (Kerr) black hole, the star and the disk contribute negligibly.

We show that no circular geodesics with constant latitude θ ≠ π 2 , stable or unstable, exist in the Kerr metric.

The material contained within a stationary black hole event horizon must satisfy the condition a/m