Ramesh Tikekar

Some exact solutions of string cosmology in Bianchi III space-time

Following the techniques used by Letelier and Stachel some exact Bianchi III cosmological solutions of massive strings in the presence of magnetic field are obtained and their physical features are discussed. Some string solutions in which magnetic fields are absent are also discussed.

Exact Relativistic Model for a Superdense Star

Assuming that the physical 3-spacet = const in a superdense star is spheroidal, a static spherically symmetric model based on an exact solution of Einstein’s equations is given which will permit densities of the order of 2 × 1014 gm cm-3, radii of the order of a few kilometers and masses up to about four times the solar mass.

Exact model for a relativistic star

Assuming that the physical three‐space in a relativistic superdense star has the geometry of a three‐spheroid, a static spherically symmetric model based on an analytic closed‐form solution of Einstein’s field equations is presented. Assuming the density of the order of 2×1014 g cm−3, estimates of the total mass and size of the stars of the model are obtained for various values of a density‐variation parameter that is suitably defined. The total mass and the boundary radius of each of these models are of the order of the mass and size of a neutron star.

Some exact solutions in Bianchi VI0 string cosmology

Following the techniques used by Letelier and Stachel some new physically relevant explicit Bianchi VI0 solutions of string cosmology with magnetic field are reported. They include two models describing distributions of Takabayashi strings and geometric strings respectively.

Relativistic fluid sphere on pseudo-spheroidal space-time

A new exact closed form solution of Einsteins field equations is reported describing the space-time in the interior of a fluid sphere in equilibrium. The physical 3-space,t=constant of its space-time has the geometry of a 3-pseudo spheroid. The suitability of this solution for describing the model of a relativistic superdense star is discussed and the stability of the model under radial pulsations is examined.

A class of cylindrically-symmetric models in string cosmology

A new class of physically relevant explicit solutions for string cosmological models endowed with cylindrical symmetry on the background of singularity-free cosmological space times has been obtained and their physical and kinematical features are discussed. The matter-free limits of this class of solutions are observed to be the singularity-free vacuum solutions of Patel and Dadhich.

Space-time inhomogeneity, anisotropy and gravitational collapse

We investigate the evolution of non-adiabatic collapse of a shear-free spherically symmetric stellar configuration with anisotropic stresses accompanied with radial heat flux. The collapse begins from a curvature singularity with infinite mass and size on an inhomogeneous space–time background. The collapse is found to proceed without formation of an even horizon to singularity when the collapsing configuration radiates all its mass energy. The impact of inhomogeneity on various parameters of the collapsing stellar configuration is examined in some specific space–time backgrounds.

Exact Interior Solutions for Charged Fluid Spheres

A new method is discussed to obtain the interior solution of Einstein-Maxwell equations for a charged static sphere from a known particular solutions of a similar kind. Beginning with a charged fluid interior solution reported by Patel and Pandya [11], a new interior Reissner-Nördstrom metric is obtained using this method and physical aspects of it are extensively discussed.

RELATIVISTIC SUPERDENSE STAR MODELS OF PSEUDO SPHEROIDAL SPACE–TIME

The physically viable models of compact stars like SAX (J1808.4-3658) can be obtained using Vaidya–Tikekar ansatz prescribing spheroidal geometry for their interior space–time. We discuss here the suitability of an alternative ansatz in this context. The models of superdense star are proposed using a general three parameter family of solutions of relativistic field equations obtained adopting the alternative ansatz. The setup is shown to admit physically viable models of superdense stars and strange matter stars such as Her. X-1.

Spherical charged fluid distributions in general relativity

Formal features of Einstein–Maxwell equations for spherically symmetric distributions of a charged perfect fluid in equilibrium are discussed. An exact solution of the system of equations for a specified choice of matter density and fluid pressure, representing a charged perfect gas is presented.