scholarly journals Possible imprints of cosmic strings in the shadows of galactic black holes

2014 ◽  
Vol 23 (07) ◽  
pp. 1450060 ◽  
Author(s):  
Vassil K. Tinchev ◽  
Stoytcho S. Yazadjiev
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Cosmic String ◽  
Cosmic Strings ◽  
Kerr Black Hole ◽  
Black Hole Spin ◽  
Deficit Angle ◽  
Spin Parameter ◽  
Shadow Cast

We examine the shadow cast by a Kerr black hole pierced by a cosmic string. The observable images depend not only on the black hole spin parameter and the angle of inclination, but also on the deficit angle yielded by the cosmic string. The dependence of the observable characteristics of the shadow on the deficit angle is explored. The imprints in the black hole shadow left by the presence of a cosmic string can serve in principle as a method for observational detection of such strings.

Bound orbits around modified Hayward black holes

2021 ◽  
Author(s):  
Bo Gao ◽  
Xue-Mei Deng
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Angular Momentum ◽  
Gravitational Field ◽  
Periodic Orbits ◽  
Kerr Black Hole ◽  
Periodic Oscillations ◽  
Test Particles ◽  
Spin Parameter ◽  
Bound Orbits

The neutral time-like particle’s bound orbits around modified Hayward black holes have been investigated. We find that both in the marginally bound orbits (MBO) and the innermost stable circular orbits (ISCO), the test particle’s radius and its angular momentum are all more sensitive to one of the parameters [Formula: see text]. Especially, modified Hayward black holes with [Formula: see text] could mimic the same ISCO radius around the Kerr black hole with the spin parameter up to [Formula: see text]. Small [Formula: see text] could mimic the ISCO of small-spinning test particles around Schwarzschild black holes. Meanwhile, rational (periodic) orbits around modified Hayward black holes have also been studied. The epicyclic frequencies of the quasi-circular motion around modified Hayward black holes are calculated and discussed with respect to the observed Quasi-periodic oscillations (QPOs) frequencies. Our results show that rational orbits around modified Hayward black holes have different values of the energy from the ones of Schwarzschild black holes. The epicyclic frequencies in modified Hayward black holes have different frequencies from Schwarzschild and Kerr ones. These might provide hints for distinguishing modified Hayward black holes from Schwarzschild and Kerr ones by using the dynamics of time-like particles around the strong gravitational field.

scholarly journals Optical properties of Kerr–Newman spacetime in the presence of plasma

2020 ◽  
Vol 80 (8) ◽  
Author(s):  
Gulmina Zaman Babar ◽  
Abdullah Zaman Babar ◽  
Farruh Atamurotov
Keyword(s):  
Black Hole ◽  
Kerr Black Hole ◽  
Field Approximation ◽  
Weak Field ◽  
Jacobi Method ◽  
Plasma Parameters ◽  
Spin Parameter ◽  
Newman Black Hole ◽  
Shadow Cast ◽  
Thermal Radiations

Abstract We have studied the null geodesics in the background of the Kerr–Newman black hole veiled by a plasma medium using the Hamilton–Jacobi method. The influence of black hole’s charge and plasma parameters on the effective potential and the generic photon orbits has been investigated. Furthermore, our discussion embodies the effects of black hole’s charge, plasma and the inclination angle on the shadow cast by the gravity with and without the spin parameter. We examined the energy released from the black hole as a result of the thermal radiations, which exclusively depends on the size of the shadow. The angle of deflection of the massless particles is also explored considering a weak-field approximation. We present our results in juxtaposition to the analogous black holes in General Relativity, particularly the Schwarzschild and Kerr black hole.

scholarly journals Polarimetric signatures of the photon ring of a black hole that is pierced by a cosmic axion string

2021 ◽  
Vol 2021 (8) ◽  
Author(s):  
Alexander Gußmann
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Formation Mechanism ◽  
Cosmic String ◽  
Cosmic Strings ◽  
Supermassive Black Holes ◽  
Rotating Black Hole ◽  
Aharonov Bohm ◽  
Polarized Photons

Abstract A black hole image contains a bright ring of photons that have closely circled the black hole on their way from the source to the detector. Here, we study the photon ring of a rotating black hole which is pierced by a global hyper-light axion-type cosmic string. We show that the coupling 𝜙F$$ \overset{\sim }{F} $$ F ~ between the axion 𝜙 and the photon can give rise to a unique polarimetric structure of the photon ring. The structure emerges due to an Aharonov-Bohm type effect that leads to a change of the polarization directions of linear polarized photons when they circle the black hole. For several parameter choices, we determine concrete polarization patterns in the ring. Measuring these patterns can provide us with a way of determining the value of the coefficient of the mixed anomaly between electromagnetism and the symmetry that gave rise to the cosmic string. Finally, we briefly review a possible formation mechanism of black holes that are pierced by cosmic strings and discuss under which conditions we can expect such objects to be present as supermassive black holes in the center of galaxies.

MULTI-BLACK HOLES SOLUTION WITH COSMIC STRINGS

2004 ◽  
Vol 19 (10) ◽  
pp. 1549-1557 ◽  
Author(s):  
F. ÖZDEMIR ◽  
N. ÖZDEMIR ◽  
B. T. KAYNAK
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Angular Momentum ◽  
Cosmic String ◽  
Circular Orbit ◽  
Cosmic Strings ◽  
De Sitter ◽  
Circular Orbits ◽  
Small Oscillations ◽  
String Models

Some black hole-cosmic string models such as Reissner–Nordström, RN–de Sitter, Kerr–Newman and multi-black holes with cosmic string are given. Energy and angular momentum of a timelike particle in circular orbits in multi-black hole space–time are calculated. The geodesic equations for the timelike particles for the far region of the multi-black hole sources are calculated and small oscillations around the circular orbit obtained. It is seen that the particle's orbit precesses like the Lens–Thirring effect.

Observing the shadow of modified gravity black hole

2017 ◽  
Vol 26 (14) ◽  
pp. 1750156 ◽  
Author(s):  
Ahmed Alhamzawi
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Modified Gravity ◽  
Kerr Black Hole ◽  
Naked Singularity ◽  
Gravity Models ◽  
Considerable Contribution ◽  
Rotating Black Holes ◽  
Shadow Cast ◽  
Modified Gravity Models

A study of the shadow cast by rotating black holes in different models of modified gravity is presented. It is shown that the size of the shadow cast depends on the modified gravity model used. The distortions of the shadow cast by modified gravity black holes are investigated and the effects are compared with the distortions cast by Kerr black hole. The shadow of a rotating black hole in modified gravity is found to be similar to the shadow cast by Kerr black hole but with different sizes and distortion effects. The naked singularity by rotating modified gravity black hole is discussed. Finally, it is shown that some modified gravity models can present a considerable contribution to the size of black hole shadow.

scholarly journals Observability of zero-angular-momentum sources near Kerr black holes

2021 ◽  
Vol 81 (9) ◽  
Author(s):  
Haopeng Yan ◽  
Minyong Guo ◽  
Bin Chen
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Angular Momentum ◽  
Efficient Method ◽  
Kerr Black Hole ◽  
Numerical Results ◽  
Escape Probability ◽  
Black Hole Spin ◽  
Source Radius ◽  
Analytical Results

AbstractWe revisit monochromatic and isotropic photon emissions from the zero-angular-momentum sources (ZAMSs) near a Kerr black hole. We investigate the escape probability of the photons that can reach to infinity and study the energy shifts of these escaping photons, which could be expressed as the functions of the source radius and the black hole spin. We study the cases for generic source radius and black hole spin, but we pay special attention to the near-horizon (near-)extremal Kerr ((near-)NHEK) cases. We reproduce the relevant numerical results using a more efficient method and get new analytical results for (near-)extremal cases. The main non-trivial results are: in the NHEK region of a (near-)extremal Kerr black hole, the escape probability for a ZAMS tends to $$\frac{7}{24}\approx 29.17\%$$ 7 24 ≈ 29.17 % , independent of the NHEK radius; at the innermost of the photon shell (IPS) in the near-NHEK region, the escape probability for a ZAMS tends to $$\begin{aligned} \frac{5}{12} -\frac{1}{\sqrt{7}} + \frac{2}{\sqrt{7}\pi }\arctan \frac{1}{\sqrt{7}}\approx 12.57\% . \end{aligned}$$ 5 12 - 1 7 + 2 7 π arctan 1 7 ≈ 12.57 % .

scholarly journals SCATTERING OF COSMIC STRINGS BY BLACK HOLES: LOOP FORMATION

2007 ◽  
Vol 16 (08) ◽  
pp. 1311-1325 ◽  
Author(s):  
FLORIAN DUBATH ◽  
MAIRI SAKELLARIADOU ◽  
CLAUDE MICHEL VIALLET
Keyword(s):  
Black Hole ◽  
Cosmic String ◽  
Cosmic Strings ◽  
Rare Event ◽  
Kerr Black Hole ◽  
Small Region ◽  
Loop Formation ◽  
Rotating Black Hole ◽  
String Loop ◽  
The Impact

We study the deformation of a long cosmic string by a nearby rotating black hole. We examine whether the deformation of a cosmic string, induced by the gravitational field of a Kerr black hole, may lead to the formation of a string loop. The segment of the string which enters the ergo-sphere of a rotating black hole gets deformed and, if it is sufficiently twisted, it can self-intersect, chopping off a loop. We find that the formation of a loop, via such a mechanism, is a rare event. It will only arise in a small region of the collision phase space, which depends on the string velocity, the impact parameter and the black hole angular momentum. We conclude that, generically, a long cosmic string is simply scattered, or captured, by a nearby rotating black hole.

scholarly journals Influence of the geometric configuration of accretion flow on the black hole spin dependence of relativistic acoustic geometry

2018 ◽  
Vol 27 (03) ◽  
pp. 1850023 ◽  
Author(s):  
Pratik Tarafdar ◽  
Tapas K. Das
Keyword(s):  
Black Hole ◽  
Kerr Black Hole ◽  
Geometric Configuration ◽  
Surface Gravity ◽  
Linear Perturbation ◽  
Flow Profile ◽  
White Hole ◽  
Accretion Flow ◽  
Black Hole Spin ◽  
General Relativistic

Linear perturbation of general relativistic accretion of low angular momentum hydrodynamic fluid onto a Kerr black hole leads to the formation of curved acoustic geometry embedded within the background flow. Characteristic features of such sonic geometry depend on the black hole spin. Such dependence can be probed by studying the correlation of the acoustic surface gravity [Formula: see text] with the Kerr parameter [Formula: see text]. The [Formula: see text]–[Formula: see text] relationship further gets influenced by the geometric configuration of the accretion flow structure. In this work, such influence has been studied for multitransonic shocked accretion where linear perturbation of general relativistic flow profile leads to the formation of two analogue black hole-type horizons formed at the sonic points and one analogue white hole-type horizon which is formed at the shock location producing divergent acoustic surface gravity. Dependence of the [Formula: see text]–[Formula: see text] relationship on the geometric configuration has also been studied for monotransonic accretion, over the entire span of the Kerr parameter including retrograde flow. For accreting astrophysical black holes, the present work thus investigates how the salient features of the embedded relativistic sonic geometry may be determined not only by the background spacetime, but also by the flow configuration of the embedding matter.

scholarly journals Statistical Properties of Kerr BH Flywheel Model of QSOs/AGNs

2000 ◽  
Vol 195 ◽  
pp. 417-418
Author(s):  
S. Nitta
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Kerr Black Hole ◽  
Mass Function ◽  
Initial Mass Function ◽  
Number Density ◽  
Disk System ◽  
The Press ◽  
The Individual ◽  
Density Population

The aim of this work is to demonstrate the properties of the magnetospheric model around Kerr black holes, so-called the “flywheel” (rotation powered) model. The fly-wheel engine of the BH accretion disk system is applied to the statistics of QSOs/AGNs. Nitta, Takahashi, & Tomimatsu clarified the individual evolution of the Kerr black-hole fly-wheel engine, which is parameterized by black-hole mass, initial Kerr parameter, magnetic field near the horizon, and a dimensionless small parameter. We impose a statistical model for the initial mass function of an ensemble of black holes using the Press-Schechter formalism. With the help of additional assumptions, we can discuss the evolution of the luminosity function and the spatial number density (population) of QSOs/AGNs. The result explains well the decrease of very bright QSOs and decrease of population after z ~ 2.

scholarly journals Deciphering Black Hole Spin, Inclination angle & Charge From Kerr Shadow

2021 ◽  
Author(s):  
Deep Bhattacharjee
Keyword(s):  
Black Hole ◽  
Inclination Angle ◽  
Kerr Black Hole ◽  
Full Description ◽  
Underlying Theory ◽  
Black Hole Spin

The apparent shape of the black hole shadow provides a full description of the spin, the inclination angle and the charge of a Kerr black hole, without any astrophysical process or underlying theory in the astrophysical process.

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