Generalized Kerr spacetime with an arbitrary mass quadrupole moment: geometric properties versus particle motion
An exact solution of Einstein's field equations in empty space first found in 1985 by Quevedo and Mashhoon is analyzed in detail. This solution generalizes Kerr spacetime to include the case of matter with an arbitrary mass quadrupole moment and is specified by three parameters, the mass M, the angular momentum per unit mass a and the quadrupole parameter q. It reduces to the Kerr spacetime in the limiting case q = 0 and to the Erez–Rosen spacetime when the specific angular momentum a vanishes. The geometrical properties of such a solution are investigated. Causality violations, directional singularities and repulsive effects occur in the region close to the source. Geodesic motion and accelerated motion are studied on the equatorial plane which, due to the reflection symmetry property of the solution, also turns out to be a geodesic plane.
What can we extract from quasiperiodic oscillations?
In the light of the relativistic precession model, we present a detailed analysis extending the ones performed in the Schwarzschild and Kerr spacetimes. We consider the kilohertz quasiperiodic oscillations in the Hartle-Thorne spacetime which describes a rotating and deformed object. We derive analytic formulas for epicyclic frequencies in the Hartle-Thorne spacetime, and by means of these frequencies we interpret the kilohertz quasiperiodic oscillations of low-mass X-ray binaries of the atoll and Z sources, on the basis of the relativistic precession model. Particularly we perform an analysis for the Z source GX 5-1. We show that the quasiperiodic oscillations data can provide information on the parameters, namely, the mass, angular momentum and quadrupole moment of compact objects in low-mass X-ray binaries.
Measurements of ion energies in the tokamak plasma boundary
Abstract Measurements of ion energies in the boundary of tokamak plasmas in L-mode discharges and during ELMs are reviewed. A profile of the ion-to-electron temperature ratio T i / T e from the edge of the confined plasma into the scrape-off layer (SOL) is produced by compiling the available T i measurements. The picture that emerges is that in the SOL, as well as in the edge, T i is systematically higher than T e (ratios up to 10 just outside the last closed flux surface) for most plasma parameter regimes. Far SOL ELM ion energies measured in JET, and more recently in MAST and AUG, agree with the models of the ELM transients, providing strong evidence that ELM ions can reach the first wall with significant fraction of the pedestal energies.