Test particle motion around a black hole in Einstein-Maxwell-scalar theory
TL;DR: In this article, the authors explored the test particle motion around a black hole in Einstein-Maxwell-scalar (EMS) theory using three different black hole solutions within this theory.
Abstract: In this paper, we explore the test particle motion around black hole in Einstein-Maxwell-scalar (EMS) theory using three different black hole solutions within this theory We have first analyzed the spacetime curvature structure of these solutions and shown the existence of two singularities and the first one is at the center $r=0$ In black hole spacetime, there are two regions divided by the critical value of the cosmological parameter ${\ensuremath{\lambda}}_{0}$ The photon sphere around black hole in EMS theory has also been studied and found that it does not depend on cosmological parameter $\ensuremath{\lambda}$ We have analyzed the innermost stable circular orbits (ISCO) around black hole and shown that for all solutions ISCO radius for neutral particle decreases with the increase of black hole charge We have also studied the charged particle motion around the black hole where charged particle motion is considered in the presence of gravitational field and the Coulomb potential It is shown that ISCO radius for charged particles increases depending on the selected value of the coupling parameter which is in contradiction with observations of the inner edge of the accretion disks of the astrophysical black holes and can be used as powerful tool to rule out the EMS theory from consideration for the gravitational field theory It also studied the fundamental frequencies governed by test particle orbiting around black hole in EMS theory Finally, as test of black hole solution in EMS theory ISCO radii is compared with that in Kerr black hole and found that the spin parameter of Kerr can be mimic up to $a/M\ensuremath{\simeq}0936$
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TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.
Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …
33,785 citations
TL;DR: In this article, the authors studied the dynamics of neutral, electrically charged and magnetized particles around deformed electrically and magnetically charged Reissner-Nordstr\"om black holes.
Abstract: In this paper we study the dynamics of neutral, electrically charged and magnetized particles around deformed electrically and magnetically charged Reissner-Nordstr\"om black holes. For the neutral test particles motion, it is shown that the radius of the innermost stable circular orbits (ISCOs) decrease with the increase in both the black hole charge and positive spacetime deformation. It reaches up to $3.85M$ at the value of deformation parameter $\ensuremath{\epsilon}=20.45$ in Schwarzschild spacetime case ($Q=0$). In the extreme charged Reissner--Nordstrom black hole case, the ISCO decreases up to $2.26M$ at the value of deformation parameter $\ensuremath{\epsilon}=6.17$. Moreover, the negative deformation results in an increase in the ISCO radius. Comparing effects of positive deformation and the Reissner-Nordstr\"om black hole charge with spin of rotating Kerr black holes, it is shown that the extremely charged Reissner-Nordstr\"om black hole can mimic rotating Kerr black hole up to the spin parameter $a/M=0.48$, while for the positive deformation with $\ensuremath{\epsilon}=6.17$ the mimic value increases up to $a/M=0.88$ implying that the supermassive black hole M87 cannot be considered as Reissner-Nordstr\"om black hole. Using this comparison, we estimate charge of the supermassive black hole Sagittarius A* as $Q/M\ensuremath{\simeq}0.8287$ without deformation which can mimic the spin of the black hole. When the deformation $\ensuremath{\epsilon}=1$, the mimic charge increases up to $Q/M\ensuremath{\simeq}0.8926$. Our study of the energy extraction from the accretion disk shows that the maximum energy efficiency increases up to 20.02%, which is almost the same for extreme Kerr black hole case (20.6%). We have also considered the behaviour of ISCO of electrically charged particles showing that the attractive (repulsive) electrostatic interactions cause rapid increase (slightly decrease) of the ISCO radius. Finally, we have explored the dynamics of magnetized particles around deformed magnetically charged Reissner-Nordstr\"om black hole. By treating the magnetar PSR J1745-2900, orbiting the supermassive black hole Sagittarius A* as a magnetized particle, showing that the magnetic charge of pure Reissner-Nordstr\"om black hole can mimic spin of a rotating Kerr black hole up to $a/M\ensuremath{\simeq}0.82$ for the value to be in the range ${Q}_{m}/M\ensuremath{\in}(0,0.692)$. Moreover, we find that the positive values of the deformation parameter lead to shift the ISCO for the magnetized particles toward the central object.
33 citations
01 Jul 2016
TL;DR: In this article, the authors 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$\omega M^{2}\gg 1$.
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$\beta$.
30 citations
TL;DR: In this article, the innermost stable circular orbit (ISCO) radius of neutral and charged test particles was determined for axially symmetric magnetized black hole spacetime, and it was shown that the combined effect of black hole electric charge and magnetic field strongly affects the ISCO radius, thus shrinking its values.
Abstract: We investigate the dynamics of neutral and charged test particles around axially symmetric magnetized black hole spacetime. We consider its electromagnetic field in the black hole vicinity and study its impact on the dynamics of test particles. We determine the radius of the innermost stable circular orbit (ISCO) for neutral and charged test particles and show that the combined effect of black hole electric charge and magnetic field strongly affects the ISCO radius, thus shrinking its values. We also show that the ISCO radius of positively (negatively) charged particle initially gets increased (decreased) and then gets radically altered with an increase in the value of both black hole electric charge and test particle charge. It turns out that the repulsive (attractive) Coulomb force dominates over the Lorentz force arising from the black hole magnetic field. Typically, black hole rotation causes axially symmetric spacetime case. Similarly, it turns out that a magnetized black hole solution also causes axially symmetric spacetime as a consequence of the presence of magnetic field. We study a degeneracy for the value of the ISCO between the Kerr and the magnetized Reissner-Nordstr\"om black hole geometries and show that the combined effects of black hole charge and magnetic field can be mimicked by Kerr spacetime with the spin parameter up to $a/M\ensuremath{\approx}0.8$. Finally, we consider the center of mass energy of colliding particles and show that an increase in the values of black hole magnetic field and electric charge leads to high center of mass energy extracted by collision of two particles.
25 citations
TL;DR: In this article, the authors investigated circular orbits for test particles around the Schwarzschild-de Sitter (dS) black hole surrounded by perfect fluid dark matter and determined the region of circular orbits bounded by innermost and outermost stable circular orbits.
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.
25 citations
References
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TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.
Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …
33,785 citations
TL;DR: In this article, the Event Horizon Telescope was used to reconstruct event-horizon-scale images of the supermassive black hole candidate in the center of the giant elliptical galaxy M87.
Abstract: When surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. To image and study this phenomenon, we have assembled the Event Horizon Telescope, a global very long baseline interferometry array observing at a wavelength of 1.3 mm. This allows us to reconstruct event-horizon-scale images of the supermassive black hole candidate in the center of the giant elliptical galaxy M87. We have resolved the central compact radio source as an asymmetric bright emission ring with a diameter of 42 +/- 3 mu as, which is circular and encompasses a central depression in brightness with a flux ratio greater than or similar to 10: 1. The emission ring is recovered using different calibration and imaging schemes, with its diameter and width remaining stable over four different observations carried out in different days. Overall, the observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity. The asymmetry in brightness in the ring can be explained in terms of relativistic beaming of the emission from a plasma rotating close to the speed of light around a black hole. We compare our images to an extensive library of ray-traced general-relativistic magnetohydrodynamic simulations of black holes and derive a central mass of M = (6.5 +/- 0.7) x 10(9) M-circle dot. Our radio-wave observations thus provide powerful evidence for the presence of supermassive black holes in centers of galaxies and as the central engines of active galactic nuclei. They also present a new tool to explore gravity in its most extreme limit and on a mass scale that was so far not accessible.
2,589 citations
2,164 citations
TL;DR: In this article, the authors consider scale invariant theories which couple gravity to Maxwell fields and antisymmetric tensor fields with a dilaton field, and they exhibit in a unified way solutions representing black hole, space-time membrane, vortex and cosmological solutions.
1,260 citations
TL;DR: In this article, the authors present measurements of the properties of the central radio source in M87 using Event Horizon Telescope data obtained during the 2017 campaign, and find that >50% of the total flux at arcsecond scales comes from near the horizon and that the emission is dramatically suppressed interior to this region by a factor >10, providing direct evidence of the predicted shadow of a black hole.
Abstract: We present measurements of the properties of the central radio source in M87 using Event Horizon Telescope data obtained during the 2017 campaign. We develop and fit geometric crescent models (asymmetric rings with interior brightness depressions) using two independent sampling algorithms that consider distinct representations of the visibility data. We show that the crescent family of models is statistically preferred over other comparably complex geometric models that we explore. We calibrate the geometric model parameters using general relativistic magnetohydrodynamic (GRMHD) models of the emission region and estimate physical properties of the source. We further fit images generated from GRMHD models directly to the data. We compare the derived emission region and black hole parameters from these analyses with those recovered from reconstructed images. There is a remarkable consistency among all methods and data sets. We find that >50% of the total flux at arcsecond scales comes from near the horizon, and that the emission is dramatically suppressed interior to this region by a factor >10, providing direct evidence of the predicted shadow of a black hole. Across all methods, we measure a crescent diameter of 42 ± 3 μas and constrain its fractional width to be <0.5. Associating the crescent feature with the emission surrounding the black hole shadow, we infer an angular gravitational radius of GM/Dc2 = 3.8 ± 0.4 μas. Folding in a distance measurement of ${16.8}_{-0.7}^{+0.8}\,\mathrm{Mpc}$ gives a black hole mass of $M=6.5\pm 0.2{| }_{\mathrm{stat}}\pm 0.7{| }_{\mathrm{sys}}\times {10}^{9}\hspace{2pt}{M}_{\odot }$. This measurement from lensed emission near the event horizon is consistent with the presence of a central Kerr black hole, as predicted by the general theory of relativity.
1,024 citations