The second rise of general relativity in astrophysics

2019 ◽  
Vol 34 (30) ◽  
pp. 1950244
Author(s):  
L. Neslušan
Keyword(s):  
General Relativity ◽  
Outer Surface ◽  
Compact Object ◽  
Large Mass ◽  
Compact Objects ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Mathematical Basis ◽  
Symmetric Configuration ◽  
Newtonian Case

The field equations, which are the mathematical basis of the theory of general relativity, provide us with a much larger variety of solutions to model the neutron stars and other compact objects than are used in the current astrophysics. We point out some important consequences of the new kind of solutions of the field equations, which can be obtained if the astrophysical usage of general relativity is not constrained, and outline an impact of these solutions on the models of internal structure of compact objects. If general relativity is not constrained, it enables to construct the stable object, with the outer surface above the event horizon, of whatever large mass. A new concept of relativistic compact object is a consequence of newly discovered property of gravity, yielded by the field equations in a spherically symmetric configuration of matter: in comparison with the Newtonian case, a particle is more effectively attracted by a nearer than a more distant matter.

scholarly journals Compact scalar field solutions in EiBI gravity

2020 ◽  
Vol 29 (11) ◽  
pp. 2041011
Author(s):  
Victor I. Afonso
Keyword(s):  
General Relativity ◽  
Black Hole ◽  
Scalar Field ◽  
Proper Time ◽  
Compact Object ◽  
Compact Objects ◽  
Antipodal Point ◽  
Field Equations ◽  
Structural Modifications ◽  
Schwarzschild Radius

We discuss exact scalar field solutions describing gravitating compact objects in the Eddington-inspired Born–Infeld (EiBI) gravity, a member of the class of (metric-affine formulated) Ricci-based gravity (RBG) theories. We include a detailed account of the RBGs/GR correspondence exploited to analytically solve the field equations. The single parameter [Formula: see text] of the EiBI model defines two branches for the solution. The [Formula: see text] branch may be described as a “shell with no interior”, and constitutes an ill-defined, geodesically incomplete spacetime. The more interesting [Formula: see text] branch admits the interpretation of a “wormhole membrane”, an exotic horizonless compact object with the ability to transfer particles and light from any point on its surface (located slightly below the would-be Schwarzschild radius) to its antipodal point, in a vanishing fraction of proper time. This is a single example illustrating how the structural modifications introduced by the metric-affine formulation may lead to significant departures from General relativity (GR) even at astrophysically relevant scales, giving rise to physically plausible objects radically different from those we are used to think of in the metric approach, and that could act as a black hole mimickers whose shadows might present distinguishable signals.

Study of some compact objects in R + 2βT gravity

2019 ◽  
Vol 28 (16) ◽  
pp. 2040005
Author(s):  
Arfa Waseem ◽  
M. Sharif
Keyword(s):  
Stellar System ◽  
Graphical Analysis ◽  
Compact Objects ◽  
Stellar Structure ◽  
Energy Conditions ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Star Models ◽  
Mit Bag Model ◽  
Text Model

The aim of this work is to examine the nature as well as physical characteristics of anisotropic spherically symmetric stellar candidates in the context of [Formula: see text] gravity. We assume that the fluid components such as pressure and energy density are related through MIT bag model equation-of-state in the interior of stellar system. In order to analyze the structure formation of some specific star models, the field equations are constructed using Krori–Barua solution in which the unknown constants are evaluated by employing observed values of radii and masses of the considered stars. We check the consistency of [Formula: see text] model through the graphical analysis of energy conditions as well as stability of stellar structure. It is found that our considered stars show viable as well as stable behavior for this model.

Approximate solutions of the general relativity field equations with a scalar meson field

1963 ◽  
Vol 59 (4) ◽  
pp. 739-741 ◽  
Author(s):  
J. Hyde
Keyword(s):  
General Relativity ◽  
Scalar Meson ◽  
Empty Space ◽  
Approximate Solutions ◽  
Spherically Symmetric ◽  
Coordinate Transformations ◽  
Field Equations ◽  
Spherically Symmetric Solution ◽  
Image Position ◽  
Scalar Meson Field

It was shown by Birkhoff ((1), p. 253) that every spherically symmetric solution of the field equations of general relativity for empty space,may be reduced, by suitable coordinate transformations, to the static Schwarzschild form:where m is a constant. This result is known as Birkhoff's theorem and excludes the possibility of spherically symmetric gravitational radiation. Different proofs of the theorem have been given by Eiesland(2), Tolman(3), and Bonnor ((4), p. 167).

Exact solution of a static charged sphere in general relativity

1969 ◽  
Vol 47 (21) ◽  
pp. 2401-2404 ◽  
Author(s):  
S. J. Wilson
Keyword(s):  
Exact Solution ◽  
General Relativity ◽  
Gravitational Constant ◽  
The Self ◽  
Spherically Symmetric ◽  
Charged Sphere ◽  
Field Equations ◽  
First Order ◽  
Self Energy ◽  
Spherically Symmetric Distribution

An exact solution of the field equations of general relativity is obtained for a static, spherically symmetric distribution of charge and mass which can be matched with the Reissner–Nordström metric at the boundary. The self-energy contributions to the total gravitational mass are computed retaining only the first order terms in the gravitational constant.

scholarly journals Nonstatic Spherically Symmetric Solutions for a Perfect Fluid in General Relativity

1976 ◽  
Vol 29 (2) ◽  
pp. 113 ◽  
Author(s):  
N Chakravarty ◽  
SB Dutta Choudhury ◽  
A Banerjee
Keyword(s):  
General Relativity ◽  
Exact Solutions ◽  
Perfect Fluid ◽  
Dynamical Behaviour ◽  
Symmetric Distribution ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Spherically Symmetric Solutions ◽  
Spherically Symmetric Distribution ◽  
General Method

A general method is described by which exact solutions of Einstein's field equations are obtained for a nonstatic spherically symmetric distribution of a perfect fluid. In addition to the previously known solutions which are systematically derived, a new set of exact solutions is found, and the dynamical behaviour of the corresponding models is briefly discussed.

scholarly journals Nonstatic Spherically Symmetric Isotropic Solutions for a Perfect Fluid in General Relativity

1978 ◽  
Vol 31 (1) ◽  
pp. 111 ◽  
Author(s):  
Max Wyman
Keyword(s):  
Differential Equation ◽  
General Relativity ◽  
General Solution ◽  
Present Author ◽  
Spherically Symmetric ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Perfect Fluids ◽  
Specific Choice ◽  
Total Differential

The present author (Wyman 1946) showed that all perfect fluids which can be represented by nonstatic, spherically symmetric, isotropic solutions of the Einstein field equations can be found by solving a nonlinear total differential equation of the second order involving. an arbitrary function 'P(r). Since then several particular solutions of this equation have been found. Although the four solutions given recently by Chakravarty et at. (1976) involve particular choices of 'P(r), none of these is the general solution of the equation that results from the specific choice of 'P(r) that was made. The present paper shows how these four general solutions are obtained.

scholarly journals Static spherically symmetric three-form stars

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
Bruno J. Barros ◽  
Zahra Haghani ◽  
Tiberiu Harko ◽  
Francisco S. N. Lobo
Keyword(s):  
Equations Of State ◽  
Field Potential ◽  
Compact Object ◽  
Momentum Tensor ◽  
Einstein Condensate ◽  
Gravity Theory ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Potential Term ◽  
Form Field

AbstractWe consider interior static and spherically symmetric solutions in a gravity theory that extends the standard Hilbert–Einstein action with a Lagrangian constructed from a three-form field $$A_{\alpha \beta \gamma }$$ A α β γ , which generates, via the field strength and a potential term, a new component in the total energy-momentum tensor of the gravitational system. We formulate the field equations in Schwarzschild coordinates and investigate their solutions numerically for different equations of state of neutron and quark matter, by assuming that the three-field potential is either a constant or possesses a Higgs-like form. Moreover, stellar models, described by the stiff-fluid, radiation-like, bag model and the Bose–Einstein condensate equations of state are explicitly obtained in both general relativity and three-form gravity, thus allowing an in-depth comparison between the astrophysical predictions of these two gravitational theories. As a general result we find that, for all the considered equations of state, three-form field stars are more massive than their general relativistic counterparts. As a possible astrophysical application, we suggest that the 2.5$$ M_{\odot }$$ M ⊙ mass compact object, associated with the GW190814 gravitational wave event, could be in fact a neutron or a quark star described by the three-form gravity theory.

DUAL NATURE OF RICCI SCALAR AND MODELS OF THE EARLY UNIVERSE

1999 ◽  
Vol 14 (16) ◽  
pp. 1021-1031 ◽  
Author(s):  
S. K. SRIVASTAVA
Keyword(s):  
Compact Object ◽  
Gravitational Effect ◽  
High Energy ◽  
Matter Field ◽  
Compact Objects ◽  
Ricci Scalar ◽  
Field Equations ◽  
Dual Nature ◽  
Gravitational Action ◽  
High Energy Level

In some of the earlier papers, it was noticed that at a high energy level Ricci scalar behaved in dual manner: (a) like a matter field and (b) like a geometrical field. In this letter, dual nature of the Ricci scalar is also obtained from a gravitational action where R2 and R3 terms dominate the Einstein–Hilbert Lagrangian in the gravitational action. Cosmological models are derived using dual role of the Ricci scalar. In an expanding model of the universe, local gravitational effect of a compact object is ignored. These models are interesting in the sense that these have capability of exhibiting gravitational effect of compact objects also in an expanding universe. Moreover, these models provide an inhomogeneous generalization of Robertson–Walker type models. Another important feature of the letter is the derivation of these models through physical theories like phase transition and spontaneous symmetry breaking, not through conventional approach of solving complicated Einstein's field equations.

Recent developments in the tidal deformability of spinning compact objects

2016 ◽  
Vol 25 (09) ◽  
pp. 1641001
Author(s):  
Paolo Pani ◽  
Leonardo Gualtieri ◽  
Andrea Maselli ◽  
Valeria Ferrari
Keyword(s):  
General Relativity ◽  
Black Hole ◽  
Kerr Black Hole ◽  
Compact Object ◽  
Second Order ◽  
Compact Objects ◽  
Tidal Effects ◽  
First Order ◽  
Love Numbers ◽  
Recent Developments

We review recent work on the theory of tidal deformability and the tidal Love numbers of a slowly spinning compact object within general relativity. Angular momentum introduces couplings between distortions of different parity and new classes of spin-induced, tidal Love numbers emerge. Due to spin-tidal effects, a rotating object immersed in a quadrupolar, electric tidal field can acquire some induced mass, spin, quadrupole, octupole and hexadecapole moments to second-order in the spin. The tidal Love numbers depend strongly on the object’s internal structure. All tidal Love numbers of a Kerr black hole (BH) were proved to be exactly zero to first-order in the spin and also to second-order in the spin, at least in the axisymmetric case. For a binary system close to the merger, various components of the tidal field become relevant. Preliminary results suggest that spin-tidal couplings can introduce important corrections to the gravitational waveforms of spinning neutron star (NS) binaries approaching the merger.

Sign in / Sign up

Export Citation Format

Share Document