scholarly journals Accretion disks around a mass with quadrupole QUADRUPOLE

2021 ◽  
Vol 79 (1) ◽  
pp. 352-358
Author(s):  
S. Toktarbay ◽  
◽  
A.Zh. Abylaeva ◽  
G.N. Khudaibergenova ◽  
B.S. Nasyrova ◽  
...  
Keyword(s):  
Accretion Disk ◽  
Accretion Disks ◽  
Test Particle ◽  
Compact Objects ◽  
Geodesic Line ◽  
Field Equations ◽  
Schwarzschild Solution ◽  
Test Particles ◽  
Line Equation ◽  
The Stability

In this work, we consider the exterior static axisymmetric gravitational of compact objects. We investigate the properties of the q-metric which is the simplest generalization of the Schwarzschild solution that contains a quadrupole parameter. The geodesic line equation is derived from the field equations and the orbits of the test particle are investigated. We consider the stability properties of test particles moving along circular orbits around a mass with quadrupole. We show that the quadrupole modifies drastically the properties of an accretion disk made of such test particles.

scholarly journals Compact stars in f(ℛ,𝒢,𝒯 ) gravity

2021 ◽  
Vol 36 (24) ◽  
pp. 2150165
Author(s):  
M. Ilyas
Keyword(s):  
Test Particle ◽  
Gravitational Theory ◽  
Momentum Tensor ◽  
Conservation Equation ◽  
Compact Objects ◽  
Compact Stars ◽  
Energy Conditions ◽  
Field Equations ◽  
Physical Features ◽  
The Impact

This work is to introduce a new kind of modified gravitational theory, named as [Formula: see text] (also [Formula: see text]) gravity, where [Formula: see text] is the Ricci scalar, [Formula: see text] is Gauss–Bonnet invariant and [Formula: see text] is the trace of the energy–momentum tensor. With the help of different models in this gravity, we investigate some physical features of different relativistic compact stars. For this purpose, we develop the effectively modified field equations, conservation equation, and the equation of motion for test particle. Then, we check the impact of additional force (massive test particle followed by a nongeodesic line of geometry) on compact objects. Furthermore, we took three notable stars named as [Formula: see text], [Formula: see text] and [Formula: see text]. The physical behavior of the energy density, anisotropic pressures, different energy conditions, stability, anisotropy, and the equilibrium scenario of these strange compact stars are analyzed through various plots. Finally, we conclude that the energy conditions hold, and the core of these stars is so dense.

scholarly journals On The Evolution of Accretion Disks in Galactic Centers

1989 ◽  
Vol 136 ◽  
pp. 167-170
Author(s):  
Wolfgang J. Duschl
Keyword(s):  
Accretion Disk ◽  
Accretion Disks ◽  
Compact Objects ◽  
Hydrodynamical Model ◽  
Host Galaxy ◽  
Potential Well ◽  
Model Calculations ◽  
Central Object ◽  
The Galaxy ◽  
Basic Ideas

I present the results of hydrodynamical model calculations for the evolution of accretion disks in an originally soft potential well. We follow the onset of selfgravity in the accretion disk and the formation of a central object, and find that for an ample set of possible parameter combinations of the “host galaxy” the evolution runs such that today, i.e. after an evolution time of the order of 1010yrs, compact objects of about 106 M⊙ have formed in the centers of galaxies. In the first Section, I concisely describe the basic ideas; Sect. 2 is devoted to the presentation of the results of hydrodynamical model calculations; and in the last Section, I shall discuss these results, interpreting them with the help of an analytical model that shows why the evolving central object is so independent of the conditions in the galaxy.

scholarly journals Dynamics of Test Particles and Twin Peaks QPOs around Regular Black Holes in Modified Gravity

Galaxies ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 75
Author(s):  
Javlon Rayimbaev ◽  
Pulat Tadjimuratov ◽  
Ahmadjon Abdujabbarov ◽  
Bobomurat Ahmedov ◽  
Malika Khudoyberdieva
Keyword(s):  
Black Holes ◽  
Test Particle ◽  
Modified Gravity ◽  
Strong Field ◽  
Compact Objects ◽  
Precision Data ◽  
Regular Black Holes ◽  
Motion Study ◽  
Test Particles ◽  
Lower Frequencies

In this work, we have presented a detailed analysis of the event horizon of regular black holes (BHs) in modified gravity known as MOG, the so-called regular MOG BH. The motion of neutral particles around the BH has also been explored. The test particle motion study shows that the positive (negative) values of the MOG parameter mimic the spin of a rotating Kerr BH, providing the same values for the innermost stable pro-grade (retrograde) orbits of the particles in the range of the spin parameter a/M∈(−0.4125,0.6946). The efficiency of energy release from the accretion disk by the Novikov–Thorne model has been calculated, and the efficiency was shown to be linearly proportional to the increase of the MOG parameter α. Moreover, we have developed a new methodology to test gravity theories in strong-field regimes using precision data from twin-peaked quasiperiodic oscillations (QPOs) of objects calculating possible values of upper and lower frequencies. However, it is obtained that the positive MOG parameter can not mimic the spin of Kerr BHs in terms of the same QPO frequencies. We have provided possible ranges for upper and lower frequencies of twin-peak QPOs with the ratio of the upper and lower frequencies of 3:2 around regular MOG BHs in the different models. Moreover, as an example, we provide detailed numerical analysis of the QPO of GRS 1915+105 with the frequencies νU=168±5Hz and νL=113±3Hz. It is shown that the central BH of the QPO object can be a regular MOG BH when the value of the parameter is α=0.2844−0.1317+0.0074 and shines in the orbits located at the distance r/M=7.6322−0.0826+0.0768 from the central BH. It is also shown that the orbits where QPOs shine are located near the innermost stable circular orbit (ISCO) of the test particle. The correlation between the radii of ISCO and the QPO orbits is found, and it can be used as a new theoretical way to determine ISCO radius through observational data from the QPOs around various compact objects.

scholarly journals An analytical anisotropic compact stellar model of embedding class I

2021 ◽  
Vol 36 (05) ◽  
pp. 2150028
Author(s):  
Lipi Baskey ◽  
Shyam Das ◽  
Farook Rahaman
Keyword(s):  
Radial Pressure ◽  
Stellar Model ◽  
Compact Objects ◽  
Compact Stars ◽  
Model Parameters ◽  
Field Equations ◽  
Principal Stresses ◽  
Schwarzschild Solution ◽  
Spherical Fluid ◽  
Physical Profile

A class of solutions of Einstein field equations satisfying Karmarkar embedding condition is presented which could describe static, spherical fluid configurations, and could serve as models for compact stars. The fluid under consideration has unequal principal stresses i.e. fluid is locally anisotropic. A certain physically motivated geometry of metric potential has been chosen and codependency of the metric potentials outlines the formation of the model. The exterior spacetime is assumed as described by the exterior Schwarzschild solution. The smooth matching of the interior to the exterior Schwarzschild spacetime metric across the boundary and the condition that radial pressure is zero across the boundary lead us to determine the model parameters. Physical requirements and stability analysis of the model demanded for a physically realistic star are satisfied. The developed model has been investigated graphically by exploring data from some of the known compact objects. The mass-radius (M-R) relationship that shows the maximum mass admissible for observed pulsars for a given surface density has also been investigated. Moreover, the physical profile of the moment of inertia (I) thus obtained from the solutions is confirmed by the Bejger–Haensel concept.

scholarly journals Atomic X-ray spectroscopy of accreting black holes

2005 ◽  
Vol 83 (12) ◽  
pp. 1179-1242 ◽  
Author(s):  
D A Liedahl ◽  
D F Torres
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Accretion Disk ◽  
Accretion Disks ◽  
Strong Field ◽  
Electromagnetic Spectrum ◽  
Field Equations ◽  
X Ray ◽  
Physical Conditions ◽  
Luminous Objects

Current astrophysical research suggests that the most persistently luminous objects in the Universe are powered by the flow of matter through accretion disks onto black holes. Accretion disk systems are observed to emit copious radiation across the electromagnetic spectrum, each energy band providing access to rather distinct regimes of physical conditions and geometric scale. X-ray emission probes the innermost regions of the accretion disk, where relativistic effects prevail. While this has been known for decades, it also has been acknowledged that inferring physical conditions in the relativistic regime from the behavior of the X-ray continuum is problematic and not satisfactorily constraining. With the discovery in the 1990s of iron X-ray lines bearing signatures of relativistic distortion came the hope that such emission would more firmly constrain models of disk accretion near black holes, as well as provide observational criteria by which to test general relativity in the strong field limit. Here, we provide an introduction to this phenomenon. While the presentation is intended to be primarily tutorial in nature, we aim also to acquaint the reader with trends in current research. To achieve these ends, we present the basic applications of general relativity that pertain to X-ray spectroscopic observations of black hole accretion-disk systems, focusing on the Schwarzschild and Kerr solutions to the Einstein field equations. To this, we add treatments of the fundamental concepts associated with the theoretical and modeling aspects of accretion disks, as well as relevant topics from observational and theoretical X-ray spectroscopy.PACS Nos.: 32.30.Rj, 32.80.Hd, 95.30.Dr, 95.30.Sf, 95.85.Nv, 97.10.Gz. 97.80.Jp, 98.35.Mp, 98.62.Mw

scholarly journals Spherically symmetric anisotropic charged solution under complete geometric deformation approach

2021 ◽  
Vol 81 (8) ◽  
Author(s):  
S. K. Maurya ◽  
Asma Mohammed Al Aamri ◽  
Athari Khalifa Al Aamri ◽  
Riju Nag
Keyword(s):  
Systematic Approach ◽  
Compact Objects ◽  
System Of Equations ◽  
Field Equations ◽  
Stellar Objects ◽  
Spacetime Geometry ◽  
Geometric Deformation ◽  
Physical Validity ◽  
The Stability ◽  
The Impact

AbstractWe present a new systematic approach to find the exact gravitationally decoupled anisotropic spherical solution in the presence of electric charge by using the complete geometric deformation (CGD) methodology. To do this, we apply the transformations over both gravitational potentials by introducing two unknown deformation functions. This new systematic approach allows us to obtain the exact solution of the field equations without imposing any particular ansatz for the deformation functions. Specifically, a well-known mimic approach and equation of state (EOS) have been applied together for solving the system of equations, which determine the radial and temporal deformation functions, respectively. The matching conditions at the boundary of the stellar objects with the exterior Reissner–Nordström metric are discussed in detail. In order to see the physical validity of the solution, we used well-behaved interior seed spacetime geometry and solved the system of equations using the above approaches. Next, we presented several physical properties of the solution through their graphical representations. The stability and dynamical equilibrium of the solution have been also discussed. Finally, we predicted the radii and mass-radius ratio for several compact objects for different decoupling parameters together with the impact of the decoupling parameters on the thermodynamical observables.

The radial–azimuthal instability of accretion disk with anomalous viscosity

2014 ◽  
Vol 92 (5) ◽  
pp. 395-400
Author(s):  
Yue Qi Chen ◽  
Wei Qun Jiang
Keyword(s):  
Numerical Simulations ◽  
Accretion Disk ◽  
Accretion Disks ◽  
Radiation Pressure ◽  
Gas Pressure ◽  
Thermal Mode ◽  
Acoustic Modes ◽  
Anomalous Viscosity ◽  
The Stability ◽  
Inner Region

The stability of the accretion disk is solved by numerical simulations when the radial and azimuthal perturbations are considered, where we adopt the anomalous viscosity model, which is close to real accretion disks. The results are discussed in the inner, intermediate, and outer regions of the accretion disk, respectively. With the increase of viscosity, α, the thermal mode and the viscous mode, as well as the acoustic modes, become more unstable in the disk dominated by radiation pressure (inner region). The instability is also influenced by the azimuthal perturbation wavenumber, n. With the increase of n, the thermal mode becomes more unstable, while the in-mode and out-mode become more stable no matter if the disk is dominated by radiation pressure or by gas pressure (intermediate and outer regions). There are many differences between our results and others’ results, especially in the inner region of the disk, when the anomalous viscosity is considered.

scholarly journals Passing the Einstein–Rosen bridge

2014 ◽  
Vol 29 (17) ◽  
pp. 1450090 ◽  
Author(s):  
M. O. Katanaev
Keyword(s):  
Test Particle ◽  
Degrees Of Freedom ◽  
Geodesic Line ◽  
Geodesic Completeness ◽  
Test Particles ◽  
Gauge Degree ◽  
Particles Trajectories

A test particle moving along geodesic line in a spacetime has three physical propagating degrees of freedom and one unphysical gauge degree. We relax the requirement of geodesic completeness of a spacetime. Instead, we require test particles trajectories to be smooth and complete only for physical degrees of freedom. Test particles trajectories for Einstein–Rosen bridge are proved to be smooth and complete in the physical sector, and particles can freely penetrate the bridge in both directions.

scholarly journals Gravitomagnetic effects of a massive and slowly rotating sphere with an equatorial mass current on orbiting test particles

2009 ◽  
Vol 5 (S261) ◽  
pp. 152-154
Author(s):  
Leonardo Castañeda ◽  
Fernando Fandiño ◽  
William Almonacid ◽  
Edilberto Suárez ◽  
Giovanni Pinzón
Keyword(s):  
Test Particle ◽  
Equatorial Plane ◽  
Spherical Body ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Rotating Sphere ◽  
Test Particles ◽  
Particle Orbits

AbstractWithin the framework of linearized Einstein field equations we compute the gravitomagnetic effects on a test particle orbiting a slowly rotating, spherical body with a rotating matter ring fixed to the equatorial plane. Our results show that the effect on the precession of particle orbits is increased by the presence of the ring.

scholarly journals Accretion Disk Coronae

1989 ◽  
Vol 8 ◽  
pp. 535-538
Author(s):  
Max Kuperus
Keyword(s):  
Black Holes ◽  
Neutron Stars ◽  
Accretion Disk ◽  
Accretion Disks ◽  
Magnetic Activity ◽  
Compact Objects ◽  
Time Variability ◽  
X Ray ◽  
Coronal Structures

SummaryAccretion disk coronae around compact objects are the result of strong magnetic activity in the inner regions of accretion disks. Part of the accreting energy is dissipated in te corona and can be observed as hard X-ray emission with a time variability caused by the coronal structures. The interaction of disk coronae with neutron stars and black holes may cause quaslperiodlc oscillations respectively flare type emission.

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