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 Bootstrapped Newtonian stars and black holes

2019 ◽  
Vol 79 (11) ◽  
Author(s):  
Roberto Casadio ◽  
Michele Lenzi ◽  
Octavian Micu
Keyword(s):  
Black Holes ◽  
Gravitational Potential ◽  
Strong Field ◽  
Compact Objects ◽  
Newtonian Gravity ◽  
Speed Of Light ◽  
Relativistic Case ◽  
Test Particles ◽  
Equilibrium Configurations ◽  
General Relativistic

Abstract We study equilibrium configurations of a homogenous ball of matter in a bootstrapped description of gravity which includes a gravitational self-interaction term beyond the Newtonian coupling. Both matter density and pressure are accounted for as sources of the gravitational potential for test particles. Unlike the general relativistic case, no Buchdahl limit is found and the pressure can in principle support a star of arbitrarily large compactness. By defining the horizon as the location where the escape velocity of test particles equals the speed of light, like in Newtonian gravity, we find a minimum value of the compactness for which this occurs. The solutions for the gravitational potential here found could effectively describe the interior of macroscopic black holes in the quantum theory, as well as predict consequent deviations from general relativity in the strong field regime of very compact objects.

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 Strong-field gravitational-wave emission in Schwarzschild and Kerr geometries: some general considerations

2018 ◽  
Vol 168 ◽  
pp. 02006 ◽  
Author(s):  
J.F. Rodríguez ◽  
J.A. Rueda ◽  
R. Ruffini
Keyword(s):  
Black Hole ◽  
Test Particle ◽  
Strong Field ◽  
Reaction Force ◽  
Dynamical Evolution ◽  
Radiation Reaction ◽  
Compact Objects ◽  
Einstein Equations ◽  
Smooth Transition ◽  
Wave Emission

We have used the perturbations of the exact solutions of the Einstein equations to estimate the relativistic wave emission of a test particle orbiting around a black hole. We show how the hamiltonian equations of motion of a test particle augmented with the radiation-reaction force can establish a priori constraints on the possible phenomena occurring in the merger of compact objects. The dynamical evolution consists of a helicoidal sequence of quasi-circular orbits, induced by the radiation-reaction and the background spacetime. Near the innermost stable circular orbit the evolution is followed by a smooth transition and finally plunges geodesically into the black hole horizon. This analysis gives physical insight of the merger of two equal masses objects.

scholarly journals Exotic orbits due to spin–spin coupling around Kerr black holes

2017 ◽  
Vol 27 (01) ◽  
pp. 1750179 ◽  
Author(s):  
Wen-Biao Han ◽  
Shu-Cheng Yang
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Equatorial Plane ◽  
Strong Field ◽  
Kerr Black Hole ◽  
Spin Coupling ◽  
Spinning Particles ◽  
Test Particles ◽  
Kerr Black Holes ◽  
Large Spins

We report exotic orbital phenomena of spinning test particles orbiting around a Kerr black hole, i.e. some orbits of spinning particles are asymmetrical about the equatorial plane. When a nonspinning test particle orbits around a Kerr black hole in a strong field region, due to relativistic orbital precessions, the pattern of trajectories is symmetrical about the equatorial plane of the Kerr black hole. However, the patterns of the spinning particles’ orbit are no longer symmetrical about the equatorial plane for some orbital configurations and large spins. We argue that these asymmetrical patterns come from the spin–spin interactions between spinning particles and Kerr black holes, because the directions of spin–spin forces can be arbitrary, and distribute asymmetrically about the equatorial plane.

scholarly journals A pseudo-Newtonian description of any stationary space-time

2016 ◽  
Vol 12 (S324) ◽  
pp. 45-46
Author(s):  
Vojtěch Witzany ◽  
Claus Lämmerzahl
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Strong Field ◽  
Kerr Black Hole ◽  
Space Time ◽  
Schwarzschild Black Hole ◽  
Test Particles ◽  
Kerr Field ◽  
Alternative Gravity Theories ◽  
Static Space

AbstractSince the first investigations into accretion onto black holes, astrophysicists have proposed effective Newtonian-like potentials to mimic the strong-field behavior of matter near a Schwarzschild or Kerr black hole. On the other hand, the fields of neutron stars or black holes in many of the alternative gravity theories differ from the idealized Schwarzschild or Kerr field which would require a number of new potentials. To resolve this, we give a Newtonian-like Hamiltonian which almost perfectly mimics the behavior of test particles in any given stationary space-time. The properties of the Hamiltonian are excellent in static space-times such as the Schwarzschild black hole, but become worse for space-times with gravito-magnetic or dragging effects such as near the Kerr black hole.

scholarly journals Stability of regular black holes and other compact objects with a charged de Sitter core and a surface matter layer

2021 ◽  
Vol 103 (10) ◽  
Author(s):  
Angel D. D. Masa ◽  
Enesson S. de Oliveira ◽  
Vilson T. Zanchin
Keyword(s):  
Black Holes ◽  
Compact Objects ◽  
De Sitter ◽  
Regular Black Holes

scholarly journals Testing cosmic censorship conjecture near extremal black holes with cosmological constants

2014 ◽  
Vol 23 (05) ◽  
pp. 1450044 ◽  
Author(s):  
Yuan Zhang ◽  
Sijie Gao
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Test Particle ◽  
Kerr Black Hole ◽  
Radiation Reaction ◽  
Cosmic Censorship ◽  
De Sitter ◽  
Test Particles ◽  
Cosmological Constants ◽  
Cosmic Censorship Conjecture

It has been shown previously that an extremal Reissner–Nordström or an extremal Kerr black hole cannot be overcharged or overspun by a test particle, if radiative and self-force effects are neglected. In this paper, we consider extremal charged and rotating black holes with cosmological constants. By studying the motion of test particles, we find the following results: An extremal Reissner–Nordström anti-de Sitter (RN–AdS) black hole can be overcharged by a test particle but an extremal Reissner–Nordström de Sitter (RN–dS) black hole cannot be overcharged. We also show that both extremal Kerr–de Sitter (Kerr–dS) and Kerr–anti-de Sitter (Kerr–AdS) black holes can be overspun by a test particle, implying a possible breakdown of the cosmic censorship conjecture. For the Kerr–AdS case, the overspinning requires that the energy of the particle be negative, a reminiscent of the Penrose process. In contrast to the extremal RN and Kerr black holes, in which cases the cosmic censorship is upheld, our results suggest some subtle relations between the cosmological constants and the cosmic censorship. We also discuss the effect of radiation reaction for the Kerr–dS case and find that the magnitude of energy loss due to gravitational radiation may not be enough to prevent the violation of the cosmic censorship.

scholarly journals From fundamental physics to tests with compact objects in metric-affine theories of gravity

2020 ◽  
Vol 29 (11) ◽  
pp. 2041007
Author(s):  
Diego Rubiera-Garcia
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Strong Field ◽  
Compact Objects ◽  
Fundamental Physics ◽  
Theories Of Gravity

This paper provides a short but comprehensible overview of some relevant aspects of metric-affine theories of gravity in relation to the physics and astrophysics of compact objects. We shall highlight the pertinence of this approach to supersede General Relativity on its strong-field regime, as well as its advantages and some of its difficulties. Moreover, we shall reflect on the present and future opportunities to test its predictions with relativistic and nonrelativistic stars, black holes, and other exotic horizonless compact objects.

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