arXiv subjects

Jacob Biemond

Publications and source records attributed to Jacob Biemond.

5 recordsLinked to original sources

arXiv2012

The gravitomagnetic field of a sphere, Gravity Probe B and the LAGEOS satellites

The gravitomagnetic field generated by a rotating sphere is usually calculated from the ideal dipole model. However, for a sphere with a homogeneous mass density, this model is not generally valid. Trying to obtain a more accurate value of the gravitomagnetic field inside and outside the sphere, series expansions for this field are presented in this paper. The calculated polar gravitomagnetic field of the sphere and that from the ideal dipole model appear to coincide, but the field in the vicinity of the sphere may deviate. The deduced field within the sphere strongly deviates from the ideal dipole result. As an illustration, the gravitomagnetic precession rate (or frame-dragging effect) of a gyroscope moving in the gravitomagnetic field from a large rotating sphere is calculated. For the Gravity Probe B experiment the result may coincide with the prediction from the ideal dipole model and in fair agreement with observations. In addition, the obtained Lense-Thirring precession rate for the LAGEOS satellites probably coincides with the standard prediction. For both experiments alternative predictions are calculated, when the gravitomagnetic field and the magnetic field from moving charge are equivalent. Theoretical and observational indications for such an equivalence are summarized. The obtained series expansions for the gravitomagnetic field of a sphere can also be applied to the calculation of the magnetic field, generated by a rotating sphere with a homogeneous charge density. Results for this case are also discussed.

physics.gen-ph↗

arXiv2009

Quasi-periodic oscillations, charge and the gravitomagnetic theory

A new model for the explanation of the high frequency quasi-periodic oscillations (QPOs) in pulsars, black holes and white dwarfs is presented. Three circular tori are assumed to be present around the star: an inner torus with charge $Q_i$, an outer torus with charge $Q_o$ and a torus with electrically neutral mass $m_m$ in the middle, whereas the star bears a charge $Q_s$ ($Q_o$ and $Q_s$ have the same sign, $Q_i$ the opposite one). The frequency $ν_m$ of the mass current is approximately given by the Kepler frequency, whereas the frequencies of $Q_i$ and $Q_o$, $ν_i$ and $ν_o$, respectively, are calculated from classical mechanics and Coulomb's law. For the explanation of the low frequency QPOs in pulsars and black holes a special interpretation of the gravitomagnetic theory may be essential. From the latter theory four new gravitomagnetic precession frequencies are deduced, which may be identified with the observed low frequency QPOs. Predictions of the presented model are compared with observed high frequency and low frequency QPOs of the pulsars SAX J1808.4--3658, XTE J1807--294, IGR J00291+5934, SGR 1806--20 and the black hole XTE J1550--564. In addition, charge flow near the pole of pulsars may explain frequency drift of burst oscillations. Moreover, charge flow at the equator of SAX J1808.4--3658 may be the cause of the enigmatic 410 kHz QPO. Furthermore, the Lense-Thirring frequency is discussed and a modified formula is compared with data of the pulsars. Contrary to pulsars and black holes, the low frequency QPOs of white dwarfs might be attributed to electromagnetic precession frequencies, deduced in this work. Predictions are compared with data of the dwarf nova VW Hyi.

physics.gen-ph↗

arXiv2004

Which gravitomagnetic precession rate will be measured by Gravity Probe B?

General relativity predicts a "hyperfine" precession rate for a gyroscope moving in the gravitomagnetic field of a rotating massive body. The recently launched Gravity Probe B (GP-B) will test the predicted precession rate of 40.9 milliarc-seconds per year for a set of four gyroscopes in a Polar Earth Orbit (PEO). It may be possible, however, that the gravitomagnetic field from a rotating mass behaves in the same way as the magnetic field generated by a moving charge. In that case the predicted precession rate of a gyroscope will be zero, since the gyroscopes of GP-B have been shielded against external magnetic fields. Another possible manifestation of the equivalence of gravitomagnetic and magnetic field may already have been found. It is the so-called Wilson Blackett law, approximately describing the magnetic field of many rotating celestial bodies. In this work a review of the gravitomagnetic approach is given starting from the Einstein equations. Four gravitomagnetic equations, analogous to the Maxwell equations, are deduced. The Wilson Blackett relation follows from these equations, if the gravitomagnetic field is identified as a common magnetic field. In addition, the precession rate for a gyroscope in terms of the gravito-magnetic field has been derived, starting from the principle of general covariance. The gravitomagnetic field may again be identified as a common magnetic field, or can be evaluated in the standard way. The future observations from GP-B may discriminate between the alternative choices.

physics.gen-ph↗

arXiv2004

The magnetic field of pulsars and the gravito-magnetic theory

Many authors have considered a gravitational origin of the magnetic field of celestial bodies. Especially, the so-called Wilson-Blackett formula has been investigated, both theoretically and observationally. It appeared possible to deduce this formula from general relativity, e. g., by application of a special interpretation of gravito-magnetic theory. More consequences of the latter theory for pulsars will be considered in this work. As an example, the standard quadrupolar charge density for pulsars can be deduced from the gravito-magnetic theory. Moreover, a new magnetic dipole moment from electromagnetic origin is found, generated in the basic magnetic field from gravito-magnetic origin. In general, for thirteen accreting, slowly rotating, binary pulsars the agreement between the observed magnetic field and the gravito-magnetic prediction is better than between the observed value and the value from the standard magnetic dipole radiation model. At present, an analogous comparison for five isolated pulsars appears to be difficult. For a sample of 100 pulsars the averaged (gravito-)magnetic field, extracted from the magnetic dipole spin-down model, is in fair agreement with the gravito-magnetic prediction. Unfortunately, the (gravito-)magnetic field has not yet directly been measured. Finally, it is found that the first and second order braking indices only depend on the magnetic field from electromagnetic origin.

astro-ph↗

arXiv2001

Are electromagnetic phenomena derivable from extended Einstein equations?

A new term describing interactions between charge and potentials may be added to the right hand side of the Einstein equations. In the proposed term an additional tensor has been introduced containing a charge density, analogous to the energy-momentum tensor containing a mass density. (The contribution of the electromagnetic fields has not been considered in this work.) The metric components in the new equations may contain charge and mass contributions. In the special relativistic case a set of four vacuum Maxwell equations is obtained from the new equations containing a special relativistic charge density. A related result was recently found by Jefimenko from a special relativistic transformation. Moreover, from the postulated equations the usual special relativistic electric energy and Lorentz force can be calculated, when the approximated electromagnetic metric is used. In the non-relativistic case the usual Maxwell equations with rest charge density are obtained. In the presence of a static gravitational field a set of four Maxwell equations is obtained applying in the general relativistic case. From these equations the generally accepted isotropic velocity of light can be deduced. In addition, calculated generalized Maxwell equations show that vacuum permittivity and permeability may differ from unity value in the presence of a big charge Q or a big mass M.

physics.gen-ph↗