Abstract: This work is devoted to study the effects of Einstein-AEther gravity on the dynamics of magnetized particles orbiting a static, spherically symmetric and uncharged black hole immersed in an external asymptotically uniform magnetic field in both comoving and proper observers frames. The analysis is carried out by varying the free parameters c 13 and c 14 of the Einstein-AEther theory and noticing their impacts on the particle trajectories, radii of the innermost stable circular orbits (ISCOs), and the amount of center-of-mass energy produced as a result of the collision. The strength of the magnetic field and the location of circular orbits is significantly affected by varying the above free parameters. We have also made detailed comparisons between the effects of parameters of Einstein-AEther and spin of rotating Kerr black holes on ISCO followed by magnetized particles and noticed that both black holes depict similar behavior for suitable values of c 13 , c 14 , spin and the magnetic coupling parameters which provide exactly the same values for the ISCO. Finally, we have analyzed the cases when a static AEther black hole can be described as Schwarzschild black hole in modified gravity (MOG) with the corresponding values of the parameters of the black holes.

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Topics: Black hole (66%), Schwarzschild metric (56%), Magnetic field (51%)

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10 results found

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01 Jul 2016-

Abstract: We have studied the orbits of magnetized particles around Hořava-Lifshitz black hole with mass M$M$ immersed in an asymptotically uniform magnetic field in the infrared approximation when ωM2≫1$\omega M^{2}\gg 1$. It is shown that magnetized particle’s orbit in Hořava-Lifshitz spacetime is different with compare to one in Schwarzschild spacetime due to the presence of additional terms related to the Kehagias-Sfetsos (KS) parameter ω$\omega$. Using the Hamilton-Jacobi formalism, we have found the dependence of the area of stable circular orbits of the magnetized particle on dimensionless KS parameter ω˜$\tilde{\omega}$ and have plotted them for several values of magnetic coupling parameter β$\beta$ as well as obtained the equations of motion of the magnetized particle. Moreover, we have studied the dependence of the collision of (magnetized, charged, non-charged) particles on KS parameter ω$\omega$ for some fixed values of the magnetic coupling parameter β$\beta$.

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Topics: Black hole (63%)

26 Citations

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29 Oct 2020-

Abstract: In the present work we explored the dynamics of magnetized particles around the compact object in γ-spacetime in the presence of an external asymptotically-uniform magnetic field. The analysis of the circular orbits of magnetized particles around the compact object in the spacetime of a γ-object immersed in the external magnetic field has shown that the area of stable circular orbits of magnetized particles increases with the increase of γ-parameter. We have also investigated the acceleration of the magnetized particles near the γ-object and shown that the center-of-mass energy of colliding magnetized particles increases with the increase of γ-parameter. Finally, we have applied the obtained results to the astrophysical scenario and shown that the values of γ-parameter in the range of γ∈(0.5,1) can mimic the spin of Kerr black hole up to a≃0.85, while the magnetic interaction can mimic the γ-parameter at γ∈(0.8,1) and spin of a Kerr black hole up to a≃0.3.

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Topics: Rotating black hole (55%), Magnetosphere particle motion (53%), Magnetic field (53%) ... show more

13 Citations

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Abstract: In this paper, we investigate circular orbits for test particles around the Schwarzschild–de Sitter (dS) black hole surrounded by perfect fluid dark matter. We determine the region of circular orbits bounded by innermost and outermost stable circular orbits. We show that the impact of the perfect fluid dark matter shrinks the region where circular orbits can exist as the values of both innermost and outermost stable circular orbits decrease. We find that for specific lower and upper values of the dark matter parameter there exist double matching values for inner and outermost stable circular orbits. It turns out that the gravitational attraction due to the dark matter contribution dominates over cosmological repulsion. This gives rise to a remarkable result in the Schwarzschild–de Sitter black hole surrounded by dark matter field in contrast to the Schwarzschild–de Sitter metric. Finally, we study epicyclic motion and its frequencies with their applications to twin peak quasi-periodic oscillations (QPOs) for various models. We find the corresponding values of the black hole parameters which could best fit and explain the observed twin peak QPO object GRS 1915+109 from microquasars.

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Topics: Schwarzschild radius (59%), Black hole (58%), Dark matter (55%) ... show more

2 Citations

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Abstract: In this paper we investigate circular orbits for test particles around Schwarzschild-de Sitter (dS) black hole surrounded by perfect fluid dark matter. We determine the region of circular orbits bounded by innermost and outermost stable circular orbits. We show that the impact of the perfect fluid dark matter shrinks the region where circular orbits can exist as the values of both innermost and outermost stable circular orbits decrease. We find that for specific lower and upper values of dark matter parameter there exist double matching values for inner and outermost stable circular orbits. It turns out that the gravitational attraction due to the dark matter contribution dominates over cosmological repulsion. This gives rise to a remarkable result in the Schwarzschild-dS black hole surrounded by dark matter field in contrast to the Schwarzschild-dS metric. Finally, we study epicyclic motion and its frequencies with their applications to twin peak quasi-periodic oscillations (QPO) for various models. We find corresponding values of the black hole parameters which could best fit and explain the observed twin peak QPO object GRS 1915+109 from microquasars.

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Topics: Schwarzschild radius (60%), Black hole (59%), Dark matter (56%) ... show more

2 Citations

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Abstract: We study spherically symmetric spacetimes in Einstein-aether theory in three different coordinate systems, the isotropic, Painleve-Gullstrand, and Schwarzschild coordinates, in which the aether is always comoving, and present both time-dependent and time-independent exact vacuum solutions. In particular, in the isotropic coordinates we find a class of exact static solutions characterized by a single parameter c14 in closed forms, which satisfies all the current observational constraints of the theory, and reduces to the Schwarzschild vacuum black hole solution in the decoupling limit (c14=0). However, as long as c14≠0, a marginally trapped throat with a finite non-zero radius always exists, and on one side of it the spacetime is asymptotically flat, while on the other side the spacetime becomes singular within a finite proper distance from the throat, although the geometric area is infinitely large at the singularity. Moreover, the singularity is a strong and spacetime curvature singularity, at which both of the Ricci and Kretschmann scalars become infinitely large.

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Topics: Schwarzschild coordinates (66%), Isotropic coordinates (63%), Schwarzschild radius (59%) ... show more

2 Citations

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85 results found

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Abstract: We study a generally covariant model in which local Lorentz invariance is broken by a dynamical unit timelike vector field ${u}^{a}$---the ``aether.'' Such a model makes it possible to study the gravitational and cosmological consequences of preferred frame effects, such as ``variable speed of light'' or high frequency dispersion, while preserving a generally covariant metric theory of gravity. In this paper we restrict attention to an action for an effective theory of the aether which involves only the antisymmetrized derivative ${\ensuremath{
abla}}_{[a}{u}_{b]}.$ Without matter this theory is equivalent to a sector of the Einstein-Maxwell-charged dust system. The aether has two massless transverse excitations, and the solutions of the model include all vacuum solutions of general relativity (as well as other solutions). However, the aether generally develops gradient singularities which signal a breakdown of this effective theory. Including the symmetrized derivative in the action for the aether field may cure this problem.

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Topics: Einstein aether theory (64%), Aether drag hypothesis (62%), Preferred frame (60%) ... show more

782 Citations

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Abstract: Using the fact that a Killing vector in a vacuum spacetime serves as a vector potential for a Maxwell test field, we derive the solution for the electromagnetic field occurring when a stationary, axisymmetric black hole is placed in an originally uniform magnetic field aligned along the symmetry axis of the black hole. It is shown that a black hole in a magnetic field will selectively accrete charges until its charge becomes $Q=2{\mathrm{Bb}}_{0}J$, where ${B}_{0}$ is the strength of the magnetic field and $J$ is the angular momentum of the black hole. As a by-product of the analysis given here, we prove that the gyromagnetic ratio of a slightly charged, stationary, axisymmetric black hole (not assumed to be Kerr) must have the value $g=2$.

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Topics: Rotating black hole (69%), Spin-flip (65%), Black hole (64%) ... show more

498 Citations

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Máximo Bañados^{1}, Máximo Bañados^{2}, Joseph Silk^{1}, Stephen M. West^{3} +1 more•Institutions (4)

Abstract: We show that intermediate mass black holes conjectured to be the early precursors of supermassive black holes and surrounded by relic cold dark matter density spikes can act as particle accelerators with collisions, in principle, at arbitrarily high center-of-mass energies in the case of Kerr black holes. While the ejecta from such interactions will be highly redshifted, we may anticipate the possibility of a unique probe of Planck-scale physics.

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Topics: Intermediate-mass black hole (67%), Binary black hole (66%), Stellar black hole (66%) ... show more

412 Citations

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Abstract: The universe is magnetized on all scales probed so far. On the largest scales, galaxies and galaxy clusters host magnetic fields at the micro Gauss level coherent on scales up to ten kpc. Recent observational evidence suggests that even the intergalactic medium in voids could host a weak ∼ 10(-16) Gauss magnetic field, coherent on Mpc scales. An intriguing possibility is that these observed magnetic fields are a relic from the early universe, albeit one which has been subsequently amplified and maintained by a dynamo in collapsed objects. We review here the origin, evolution and signatures of primordial magnetic fields. After a brief summary of magnetohydrodynamics in the expanding universe, we turn to magnetic field generation during inflation and phase transitions. We trace the linear and nonlinear evolution of the generated primordial fields through the radiation era, including viscous effects. Sensitive observational signatures of primordial magnetic fields on the cosmic microwave background, including current constraints from Planck, are discussed. After recombination, primordial magnetic fields could strongly influence structure formation, especially on dwarf galaxy scales. The resulting signatures on reionization, the redshifted 21 cm line, weak lensing and the Lyman-α forest are outlined. Constraints from radio and γ-ray astronomy are summarized. Astrophysical batteries and the role of dynamos in reshaping the primordial field are briefly considered. The review ends with some final thoughts on primordial magnetic fields.

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Topics: Reionization (58%), Structure formation (54%), Cosmic microwave background (53%) ... show more

277 Citations