Beyond general relativity models, magnetosphere structure and dark matter stars

2019 ◽  
Vol 16 (04) ◽  
pp. 1950064 ◽  
Author(s):  
D. J. Cirilo-Lombardo ◽  
F. O. Minotti
Keyword(s):  
General Relativity ◽  
Compact Object ◽  
High Energy ◽  
Compact Objects ◽  
Axially Symmetric ◽  
Spherically Symmetric Solution ◽  
Axion Field ◽  
Shafranov Equation ◽  
Symmetric Version ◽  
Energy Processes

The magnetosphere structure of compact objects is considered in the context of a theory of gravity with dynamical torsion field beyond standard General Relativity (GR). To this end, a new spherically symmetric solution is obtained in this theoretical framework, physically representing a compact object of pseudoscalar fields (for example, axion field). The axially symmetric version of the Grad–Shafranov equation (GSE) is also derived in this context, and used to describe the magnetosphere dynamics of the obtained “axion star”. The interplay between high-energy processes and the seed magnetic field with respect to the global structure of the magnetosphere is briefly discussed.

scholarly journals A large-particle Monte Carlo code for simulating non-linear high-energy processes near compact objects

1995 ◽  
Vol 272 (2) ◽  
pp. 291-307 ◽  
Author(s):  
Boris E. Stern ◽  
Mitchell C. Begelman ◽  
Marek Sikora ◽  
Roland Svensson
Keyword(s):  
Monte Carlo ◽  
Large Particle ◽  
High Energy ◽  
Compact Objects ◽  
Monte Carlo Code ◽  
Non Linear ◽  
Energy Processes

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.

scholarly journals (Self-)Magnetized Bose–Einstein condensate stars

2019 ◽  
Vol 28 (10) ◽  
pp. 1950135 ◽  
Author(s):  
G. Quintero Angulo ◽  
A. Pérez Martínez ◽  
H. Pérez Rojas ◽  
D. Manreza Paret
Keyword(s):  
Magnetic Field ◽  
Thermodynamic Description ◽  
Compact Object ◽  
Einstein Condensate ◽  
Compact Objects ◽  
Magnetic Field Effects ◽  
Axially Symmetric ◽  
Bose Einstein Condensate ◽  
Bose Einstein ◽  
The Magnetic Field

We study magnetic field effects on the Equations-of-State (EoS) and the structure of Bose–Einstein Condensate (BEC) stars, i.e. a compact object composed by a gas of interacting spin-one bosons formed up by the pairing of two neutrons. To include the magnetic field in the thermodynamic description, we assume that particle–magnetic field and particle–particle interactions are independent. We consider two configurations for the magnetic field: one where it is constant and externally fixed, and another where it is produced by the bosons through self-magnetization. Stable configurations of self-magnetized and magnetized nonspherical BEC stars are studied using structure equations that describe axially symmetric objects. In general, the magnetized BEC stars are spheroidal, less massive and smaller than the nonmagnetic ones, being these effects more relevant at low densities. Nevertheless, star masses around two solar masses are obtained by increasing the strength of the boson–boson interaction. The inner magnetic field profiles of the self-magnetized BEC stars can be computed as a function of the equatorial radii. The values obtained for the core and surface magnetic fields are in agreement with those typically found in compact objects.

scholarly journals Compact objects in general relativity: From Buchdahl stars to quasiblack holes

2020 ◽  
Vol 29 (11) ◽  
pp. 2041019 ◽  
Author(s):  
José P. S. Lemos ◽  
Oleg B. Zaslavskii
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Mass Formula ◽  
Compact Star ◽  
Compact Object ◽  
Compact Objects ◽  
Gravitational Radius ◽  
Penrose Diagram ◽  
Boundary Radius ◽  
Extremal Black Holes

A Buchdahl star is a highly compact star for which the boundary radius [Formula: see text] obeys [Formula: see text], where [Formula: see text] is the gravitational radius of the star itself. A quasiblack hole is a maximum compact star, or more generically a maximum compact object, for which the boundary radius [Formula: see text] obeys [Formula: see text]. Quasiblack holes are objects on the verge of becoming black holes. Continued gravitational collapse ends in black holes and has to be handled with the Oppenheimer–Snyder formalism. Quasistatic contraction ends in a quasiblack hole and should be treated with appropriate techniques. Quasiblack holes, not black holes, are the real descendants of Mitchell and Laplace dark stars. Quasiblack holes have many interesting properties. We develop the concept of a quasiblack hole, give several examples of such an object, define what it is, draw its Carter–Penrose diagram, study its pressure properties, obtain its mass formula, derive the entropy of a nonextremal quasiblack hole and through an extremal quasiblack hole give a solution to the puzzling entropy of extremal black holes.

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 Non-Riemmanian geometry, force-free magnetospheres and the generalized Grad-Shafranov equation

2019 ◽  
Vol 16 (01) ◽  
pp. 1950013 ◽  
Author(s):  
Diego Julio Cirilo-Lombardo
Keyword(s):  
Generalized Equation ◽  
Excess Energy ◽  
Quantum Field ◽  
Axially Symmetric ◽  
Complex Character ◽  
Function Solution ◽  
Electron Positron ◽  
Shafranov Equation ◽  
Symmetric Version ◽  
Electron Positron Pair

The magnetosphere structure of a magnetar is considered in the context of a theory of gravity with dynamical torsion field beyond the standard General Relativity (GR). To this end, the axially symmetric version of the Grad-Shafranov equation (GSE) is obtained in this theoretical framework. The resulting GSE solution in the case of the magnetosphere corresponds to a stream function containing also a pseudoscalar part. This function solution under axisymmetry presents a complex character that (as in the quantum field theoretical case) could be associated with an axidilaton field. Magnetar–pulsar mechanism is suggested and the conjecture about the origin of the excess energy due the GSE describing the magnetosphere dynamics is claimed. We also show that two main parameters of the electrodynamic processes (as described in GR framework by Goldreich and Julian (GJ) [Astrophys. J. 157 (1969) 869]) are modified but the electron-positron pair rate [Formula: see text] remains invariant. The possible application of our generalized equation (defined in a non-Riemannian geometry) to astrophysical scenarios involving emission of energy by gravitational waves, as described in the context of GR in [S. Capozziello, M. De Laurentis, I. De Martino, M. Formisano and D. Vernieri, Astrophys. Space Sci. 333 (2011) 29–35], is briefly discussed.

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.

General Relativity

2019 ◽  
Author(s):  
Steven Carlip
Keyword(s):  
General Relativity ◽  
High Energy Physics ◽  
Hamiltonian Formulation ◽  
Experimental Tests ◽  
High Energy ◽  
Gravitational Energy ◽  
Field Equations ◽  
Physics First ◽  
Condensed Matter Theory ◽  
Introductory Textbooks

This work is a short textbook on general relativity and gravitation, aimed at readers with a broad range of interests in physics, from cosmology to gravitational radiation to high energy physics to condensed matter theory. It is an introductory text, but it has also been written as a jumping-off point for readers who plan to study more specialized topics. As a textbook, it is designed to be usable in a one-quarter course (about 25 hours of instruction), and should be suitable for both graduate students and advanced undergraduates. The pedagogical approach is “physics first”: readers move very quickly to the calculation of observational predictions, and only return to the mathematical foundations after the physics is established. The book is mathematically correct—even nonspecialists need to know some differential geometry to be able to read papers—but informal. In addition to the “standard” topics covered by most introductory textbooks, it contains short introductions to more advanced topics: for instance, why field equations are second order, how to treat gravitational energy, what is required for a Hamiltonian formulation of general relativity. A concluding chapter discusses directions for further study, from mathematical relativity to experimental tests to quantum gravity.

Laser breakdown in crystalline argon as model of fast high-energy processes

1979 ◽  
Vol 9 (1) ◽  
pp. 48-51
Author(s):  
I I Ashmarin ◽  
A I Andreev ◽  
Yu A Bykovskiĭ ◽  
V A Gridin ◽  
Ya Yu Zysin
Keyword(s):  
High Energy ◽  
Laser Breakdown ◽  
Energy Processes
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