Cosmological solutions of the Friedmann type in the tensor-scalar theory of gravitation

Erevan State University. Translated from Astrofizika, Vol. 36, No. 4, pp. 583–592, October–December, 1993.     

Statified model of a neutron star

Evolutionary calculations based on realistic equations of state indicate the stratified nature of the distribution of hadron matter in the interiors of neutron stars. In the proposed model, the stratified structure of a neutron star is treated as a rigid inert core surrounded by a dynamical layer. The physical basis for the model is the concept of the stellar matter of the peripheral envelope as an elastic Fermi continuum, the motions of which are described by the equations of nuclear elastodynamics, proposed in the macroscopic theory of collective processes in laboratory nuclear physics. It is shown that the vibrational dynamics of a neutron star is characterized by two branches of gravitational—elastic, spheroidal (s-mode) and torsional (t-mode) nonradial eigenvibrations. Estimates obtained for the periods of global, gravitational nonradial modes suggest that variations in the intensity of micropulses observed in the millisecond range of the spectra of C-pulsars may be ascribed to these vibrations. The proposed two-component model of a neutron star enables one to consider a glitch in a pulsar’s radio emission as a starquake due to the passage of the companion through periastron of the binary system. Translated from Astrofizika, Vol. 42, No. 2, pp. 235–252, April–June, 1999     

Nonradial oscillations of a neutron star in an inhomogeneous hydrodynamic model

An inhomogeneous model neutron star with a variable density profile of the type ₀(r)=_c[1–(2/3)r²/R²]exp(–r²/R²) is considered, where _c is the central density, R is the star's radius, and is the inhomogeneity parameter in the radial mass distribution. This parameterization adequately reproduces the results of numerical evolutionary calculations of the density profile and enables one to obtain in analytical form the parameters of hydrostatic equilibrium and the eigenmodes of nonradial oscillations of a nonrotating neutron star, modeled by a spherical mass of incompressible, inviscid liquid. It is shown that a characteristic manifestation of the star's inhomogeneity is the presence of a stable dipole f-mode, the lowest one in the spectrum of natural oscillations. The presence of this mode serves as a general and primary criterion that evidently distinguishes all inhomogeneous hydrodynamic models from the homogeneous Kelvin model, in which the quadrupole mode is the lowest stable mode. Estimates obtained for the periods of nonradial pulsations coincide with the periods of micropulses observed in the average pulse profiles of c-pulsars. This suggests that the detected variations in emission intensity in the range of micropulse duration (on the order of 10^–4 sec) are associated with nonradial stellar oscillations.Translated from Astrofizika, Vol. 39, No. 3, pp. 475–488, July–September, 1996.     

Magneto-dipole configurations in general relativity

The solution of the system of Maxwell-Einstein equations, which determines the external gravitational and electromagnetic fields of magneto-dipole configurations, has been obtained to a quadratic approximation of magnetic momentum.