arXiv subjects

John Roumas

Publications and source records attributed to John Roumas.

2 recordsLinked to original sources

arXiv2018

Structure of Polytropic Stars in General Relativity

The inner structure of a star or a primordial interstellar cloud is a major topic in classical and relativistic physics. The impact that General Relativistic principles have on this structure has been the subject of many research papers. In this paper we consider within the context of General Relativity a prototype model for this problem by assuming that a star consists of polytropic gas. To justify this assumption we observe that stars undergo thermodynamically irreversible processes and emit heat and radiation to their surroundings. Due to the emission of this energy it is worthwhile to consider an idealized model in which the gas is polytropic. To find interior solutions to the Einstein equations of General Relativity in this setting we derive a single equation for the cumulative mass distribution of the star and use Tolman-Oppenheimer-Volkoff equation to derive formulas for the isentropic index and coefficient. Using these formulas we present analytic and numerical solutions for the polytropic structure of self-gravitating stars and examine their stability. We prove also that when the thermodynamics of a star as represented by the isentropic index and coefficient is known, the corresponding matter density within the star is uniquely determined.

gr-qc↗

arXiv2016

Spherical Isentropic Protostars in General Relativity

In the process of protostar formation, astrophysical gas clouds undergo thermodynamically irreversible processes and emit heat and radiation to their surroundings. Due the emission of this energy one can envision an idealized situation in which the gas entropy remains nearly constant. In this setting, we derive in this paper interior solutions to the Einstein equations of General Relativity for spheres which consist of isentropic gas. To accomplish this objective we derive a single equation for the cumulative mass distribution in the protostar. From a solution of this equation one can infer readily the coefficients of the metric tensor. In this paper we present analytic and numerical solutions for the structure of the isentropic self-gravitating gas. In particular we look for solutions in which the mass distribution indicates the presence of shells, a possible precursor to solar system formation. Another possible physical motivation for this research comes from the observation that gamma ray bursts are accompanied by the ejection of large amounts of thermodynamically active gas at relativistic velocities. Under these conditions it is natural to use the equations of general relativity to inquire about the structure of the ejected mass.

gr-qc↗