Omair Zubairi

Properties of high-density matter in neutron stars

This short review aims at giving a brief overview of the various states of matter that have been suggested to exist in the ultra-dense centers of neutron stars. Particular emphasis is put on the role of quark deconfinement in neutron stars and on the possible existence of compact stars made of absolutely stable strange quark matter (strange stars). Astrophysical phenomena, which distinguish neutron stars from quark stars, are discussed and the question of whether or not quark deconfinement may occur in neutron stars is investigated. Combined with observed astrophysical data, such studies are invaluable to delineate the complex structure of compressed baryonic matter and to put firm constraints on the largely unknown equation of state of such matter.

Static solutions of Einstein's field equations for compact stellar objects

In this work, we present two solutions of Einsteins field equations for compact stellar objects such as quark or neutron stars. Due to their unique stellar properties, these compact objects pose as excellent laboratories to study matter in the most extreme conditions. In part one of this paper, we solve Einsteins field equations modified for a finite value for the cosmological constant for spherically symmetric mass distributions. This solution has been presented in the literature before, but with inconsistent results. In part two, we examine the structure of deformed (non-spherical) compact objects. The stellar structure equations are derived and solved for in the limiting case of isotropic pressure and energy-density. We calculate stellar properties such as masses and radii along with pressure and density profiles for these deformed objects and investigate changes from the standard spherical models.

Self consistent models of deformed neutron stars in the framework of general relativity

Generally, over the last 75 years, since the publication of the well known papers from from R. C. Tolman (Tolman 1939) and J. R. Oppenheimer and G. M. Volkoff (Oppenheimer and Volkoff 1939), standard models of non-rotating neutron stars are modeled with the assumption that they are perfect spheres. This assumption of perfect spherical symmetry is not correct if the matter inside of neutron stars is described by a non-isotropic equation of state (EoS). Particular classes of neutron stars such as Magnetars and neutron stars that contain color superconducting quark matter cores are expected to be deformed making them oblong spheroids. In this paper, we examine the deformity of these non-spherical neutron stars by deriving the stellar structure equations in the framework of general relativity. Using a non-isotropic model for the equation of state, these stellar structure equations are solved numerically in two dimensions. We then calculate stellar properties such as masses and radii along with pressure and energy-density profiles and investigate any changes from conventional spherical models.

Stellar Structure Models of Deformed Neutron Stars

Traditional stellar structure models of non-rotating neutron stars work under the assumption that these stars are perfect spheres. This assumption of perfect spherical symmetry is not correct if the matter inside neutron stars is described by an anisotropic model for the equation of state. Certain classes of neutron stars such as Magnetars and neutron stars which contain color-superconducting quark matter cores are expected to be deformed making them oblong spheroids. In this work, we investigate the stellar structure of these deformed neutron stars by deriving stellar structure equations in the framework of general relativity. Using a non-isotropic equation of state model, we solve these structure equations numerically in two dimensions. We calculate stellar properties such as masses and radii along with pressure profiles and investigate changes from standard spherical models.