scholarly journals Testing gravity of a disformal Kerr black hole in quadratic degenerate higher-order scalar-tensor theories by quasi-periodic oscillations

2021 ◽  
Vol 2021 (06) ◽  
pp. 043
Author(s):  
Songbai Chen ◽  
Zejun Wang ◽  
Jiliang Jing
Keyword(s):  
Black Hole ◽  
Kerr Black Hole ◽  
Higher Order ◽  
Periodic Oscillations

scholarly journals Epicyclic oscillations in spinning particle motion around Kerr black hole applied in models fitting the quasi-periodic oscillations observed in microquasars and AGNs

2021 ◽  
Vol 81 (12) ◽  
Author(s):  
Misbah Shahzadi ◽  
Martin Kološ ◽  
Zdeněk Stuchlík ◽  
Yousaf Habib
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
High Frequency ◽  
Kerr Black Hole ◽  
Galactic Nuclei ◽  
Tidal Disruption ◽  
Periodic Oscillations ◽  
Spinning Particle ◽  
X Ray ◽  
Test Particles

AbstractThe study of the quasi-periodic oscillations (QPOs) of X-ray flux observed in the stellar-mass black hole (BH) binaries or quasars can provide a powerful tool for testing the phenomena occurring in strong gravity regime. We thus fit the data of QPOs observed in the well known microquasars as well as active galactic nuclei (AGNs) in the framework of the model of geodesic oscillations of Keplerian disks modified for the epicyclic oscillations of spinning test particles orbiting Kerr BHs. We show that the modified geodesic models of QPOs can explain the observational fixed data from the microquasars and AGNs but not for all sources. We perform a successful fitting of the high frequency QPOs models of epicyclic resonance and its variants, relativistic precession and its variants, tidal disruption, as well as warped disc models, and discuss the corresponding constraints of parameters of the model, which are the spin of the test particle, mass and rotation of the BH.

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.

Shadow of a disformal Kerr black hole in quadratic degenerate higher-order scalar–tensor theories

2020 ◽  
Vol 80 (12) ◽  
Author(s):  
Fen Long ◽  
Songbai Chen ◽  
Mingzhi Wang ◽  
Jiliang Jing
Keyword(s):  
Black Hole ◽  
Deformation Parameter ◽  
Kerr Black Hole ◽  
Arbitrary Spin ◽  
Higher Order ◽  
Fractal Structures ◽  
Extreme Black Hole ◽  
Spin Parameter ◽  
Result Show ◽  
Self Similar

AbstractWe have studied the shadow of a disformal Kerr black hole with an extra deformation parameter, which belongs to non-stealth rotating solutions in quadratic degenerate higher-order scalar–tensor (DHOST) theory. Our result show that the size of the shadow increases with the deformation parameter for the black hole with arbitrary spin parameter. However, the effect of the deformation parameter on the shadow shape depends heavily on the spin parameter of black hole and the sign of the deformation parameter. The change of the shadow shape becomes more distinct for the black hole with the more quickly rotation and the more negative deformation parameter. Especially, for the near-extreme black hole with negative deformation parameter, there exist a “pedicel”-like structure appeared in the shadow, which increases with the absolute value of deformation parameter. The eyebrow-like shadow and the self-similar fractal structures also appear in the shadow for the disformal Kerr black hole in DHOST theory. These features in the black hole shadow originating from the scalar field could help us to understand the non-stealth disformal Kerr black hole and quadratic DHOST theory.

scholarly journals Confronting the Models of 3 : 2 QPOs with the Evidence of Near Extreme Kerr Black Hole

2012 ◽  
Vol 8 (S290) ◽  
pp. 239-240
Author(s):  
Andrea Kotrlová ◽  
Gabriel Török ◽  
Eva Šrámková ◽  
Zdeněk Stuchlík
Keyword(s):  
Black Hole ◽  
High Frequency ◽  
Kerr Black Hole ◽  
Black Hole Mass ◽  
Tidal Disruption ◽  
Periodic Oscillations ◽  
Rotating Black Hole ◽  
Spectral Fitting ◽  
Generic Problem ◽  
The Individual

AbstractThe black hole mass and spin estimates assuming various specific models of the 3 : 2 high frequency quasi-periodic oscillations (HF QPOs) have been carried out in Török et al. (2005, 2011). Here we briefly summarize some current points. Spectral fitting of the spin a ≡ cJ/GM2 in the microquasar GRS 1915 + 105 reveals that this system can contain a near extreme rotating black hole (e.g., McClintock et al., 2011). Confirming the high value of the spin would have significant consequences for the theory of the HF QPOs. The estimate of a > 0.9 is almost inconsistent with the relativistic precession (RP), tidal disruption (TD), and the warped disc (WD) model. The epicyclic resonance (Ep) and discoseismic models assuming the c- and g- modes are instead favoured. However, consideration of all three microquasars that display the 3 : 2 HF QPOs leads to a serious puzzle because the differences in the individual spins, such as a = 0.9 compared to a = 0.7, represent a generic problem almost for any unified orbital 3:2 QPO model.

scholarly journals Exploring higher order images with Fe Kα-lines from relativistic disks: black hole spin determination and bias

2021 ◽  
Author(s):  
M Falanga ◽  
P Bakala ◽  
R La Placa ◽  
V De Falco ◽  
A De Rosa ◽  
...  
Keyword(s):  
Black Hole ◽  
Line Profile ◽  
Gravitational Lensing ◽  
Kerr Black Hole ◽  
Higher Order ◽  
Large Area ◽  
X Ray ◽  
Area Detector ◽  
Black Hole Spin ◽  
Stable Circular Orbit

Abstract We study the contributions to the relativistic Fe Kα line profile from higher order images (HOIs) produced by strongly deflected rays from the disk which cross the plunging region, located between the innermost stable circular orbit (ISCO) radius and the event horizon of a Kerr black hole. We investigate the characteristics features imprinted by the HOIs in the line profile for different black hole spins, disk emissivity laws and inclinations. We find that they extend from the red wing of the profile up to energies slightly lower than those of the blue peak, adding ∼0.4 − 1.3 per cent to the total line flux. The contribution to the specific flux is often in the ∼1 per cent to 7 per cent range, with the highest values attained for low and negative spin (a ≲ 0.3) black holes surrounded by intermediate inclination angle (i ∼ 40○) disks. We simulate future observations of a black hole X-ray binary system with the Large Area Detector of the planned X-ray astronomy enhanced X-ray Timing and Polarimetry Mission (eXTP) and find that the Fe Kα line profiles of systems accreting at ≲ 1 per cent the Eddington rate are affected by the HOI features for a range of parameters. This would provide evidence of the extreme gravitational lensing of HOI rays. Our simulations show also that not accounting for HOI contributions to the Fe Kα line profile may systematically bias measurements of the black hole spin parameter towards values higher by up to ∼0.3 than the inputted ones.

scholarly journals Testing Kerr black hole mimickers with quasi-periodic oscillations from GRO J1655-40

2021 ◽  
Vol 81 (11) ◽  
Author(s):  
Xin Jiang ◽  
Peng Wang ◽  
Haitang Yang ◽  
Houwen Wu
Keyword(s):  
Black Hole ◽  
Kerr Black Hole ◽  
Compact Object ◽  
Kerr Metric ◽  
Observation Data ◽  
Periodic Oscillations ◽  
Regular Black Hole ◽  
Rotating Black Hole ◽  
Traversable Wormholes ◽  
Limiting Case

AbstractThe measurements of quasi-periodic oscillations (QPOs) provide a quite powerful tool to test the nature of astrophysical black hole candidates in the strong gravitational field regime. In this paper, we use QPOs within the relativistic precession model to test a recently proposed family of rotating black hole mimickers, which reduce to the Kerr metric in a limiting case, and can represent traversable wormholes or regular black holes with one or two horizons, depending on the values of the parameters. In particular, assuming that the compact object of GRO J1655-40 is described by a rotating black hole mimicker, we perform a $$\chi $$ χ -square analysis to fit the parameters of the mimicker with two sets of observed QPO frequencies from GRO J1655-40. Our results indicate that although the metric around the compact object of GRO J1655-40 is consistent with the Kerr metric, a regular black hole with one horizon is favored by the observation data of GRO J1655-40.

scholarly journals Gedanken experiments at high-order approximation: Kerr black hole cannot be overspun

2021 ◽  
Vol 2021 (9) ◽  
Author(s):  
Aofei Sang ◽  
Jie Jiang
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Order Approximation ◽  
Energy Condition ◽  
Kerr Black Hole ◽  
Null Energy Condition ◽  
Higher Order ◽  
High Order ◽  
Order Perturbation ◽  
Kerr Black Holes

Abstract Sorce and Wald proposed a new version of gedanken experiments to examine the weak cosmic censorship conjecture (WCCC) in Kerr-Newmann black holes. However, their discussion only includes the second-order approximation of perturbation and there exists an optimal condition such that the validity of the WCCC is determined by the higher-order approximations. Therefore, in this paper, we extended their discussions into the high-order approximations to study the WCCC in a nearly extremal Kerr black hole. After assuming that the spacetime satisfies the stability condition and the perturbation matter fields satisfy the null energy condition, based on the Noether charge method by Iyer and Wald, we completely calculate the first four order perturbation inequalities and discuss the corresponding gedanken experiment to overspin the Kerr black hole. As a result, we find that the nearly extremal Kerr black holes cannot be destroyed under the fourth-order approximation of perturbation. Then, by using the mathematical induction, we strictly prove the nth order perturbation inequality when the first (n − 1) order perturbation inequalities are saturated. Using these results, we discuss the first 100 order approximation of the gedanken experiments and find that the WCCC in Kerr black hole is valid under the higher-order approximation of perturbation. Our investigation implies that the WCCC might be strictly satisfied in Kerr black holes under the perturbation level.

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