scholarly journals Null Geodesics and Gravitational Lensing in a Nonsingular Spacetime

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Shao-Wen Wei ◽  
Yu-Xiao Liu ◽  
Chun-E Fu
Keyword(s):  
Black Hole ◽  
Gravitational Lensing ◽  
Angular Position ◽  
Angular Separation ◽  
Null Geodesics ◽  
Astronomical Instruments ◽  
Black Hole Background ◽  
Deflection Limit ◽  
Near Future

The null geodesics and gravitational lensing in a nonsingular spacetime are investigated. According to the nature of the null geodesics, the spacetime is divided into several cases. In the weak deflection limit, we find the influence of the nonsingularity parameterqon the positions and magnifications of the images is negligible. In the strong deflection limit, the coefficients and observables for the gravitational lensing in a nonsingular black hole background and a weakly nonsingular spacetime are obtained. Comparing these results, we find that, in a weakly nonsingular spacetime, the relativistic images have smaller angular position and relative magnification but larger angular separation than those of a nonsingular black hole. These results might offer a way to probe the spacetime nonsingularity parameter and put a bound on it by the astronomical instruments in the near future.

scholarly journals Null Geodesics and Strong Field Gravitational Lensing in a String Cloud Background

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
M. Sharif ◽  
Sehrish Iftikhar
Keyword(s):  
Black Hole ◽  
Gravitational Lensing ◽  
Galactic Center ◽  
Deflection Angle ◽  
Orbital Motion ◽  
Strong Field ◽  
Schwarzschild Black Hole ◽  
Field Limit ◽  
Null Geodesics ◽  
Supermassive Black Hole

This paper is devoted to studying two interesting issues of a black hole with string cloud background. Firstly, we investigate null geodesics and find unstable orbital motion of particles. Secondly, we calculate deflection angle in strong field limit. We then find positions, magnifications, and observables of relativistic images for supermassive black hole at the galactic center. We conclude that string parameter highly affects the lensing process and results turn out to be quite different from the Schwarzschild black hole.

scholarly journals Weak and strong deflection gravitational lensing by a renormalization group improved Schwarzschild black hole

2019 ◽  
Vol 79 (12) ◽  
Author(s):  
Xu Lu ◽  
Yi Xie
Keyword(s):  
Black Hole ◽  
Renormalization Group ◽  
Gravitational Lensing ◽  
Galactic Center ◽  
Quantum Effect ◽  
Apparent Size ◽  
Great Care ◽  
Schwarzschild Black Hole ◽  
Sgr A ◽  
Near Future

AbstractWeak and strong deflection gravitational lensing by a renormalization group improved Schwarzschild black hole is investigated and its observables are found. By taking the supermassive black holes Sgr A* and M87* respectively in the Galactic Center and at the center of M87 as lenses, we estimate these observables and analyse possibility of detecting this quantum improvement. It is not feasible to distinguish such a black hole by most observables in the near future except for the apparent size of the shadow. We also note that directly using measured shadow of M87* to constrain this quantum effect requires great care.

scholarly journals Null Geodesics and Strong Field Gravitational Lensing of Black Hole with Global Monopole

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
M. Sharif ◽  
Sehrish Iftikhar
Keyword(s):  
Black Hole ◽  
Gravitational Lensing ◽  
Time Delays ◽  
Deflection Angle ◽  
Orbital Motion ◽  
Strong Field ◽  
Global Monopole ◽  
Schwarzschild Black Hole ◽  
Field Limit ◽  
Null Geodesics

We study two interesting features of a black hole with an ordinary as well as phantom global monopole. Firstly, we investigate null geodesics which imply unstable orbital motion of particles for both cases. Secondly, we evaluate deflection angle in strong field regime. We then find Einstein rings, magnifications, and observables of the relativistic images for supermassive black hole at the center of galaxy NGC4486B. We also examine time delays for different galaxies and present our results numerically. It is found that the deflection angle for ordinary/phantom global monopole is greater/smaller than that of Schwarzschild black hole. In strong field limit, the remaining properties of these black holes are quite different from the Schwarzschild black hole.

scholarly journals Constraining the spacetime spin using time delay in stationary axisymmetric spacetimes

2020 ◽  
Vol 80 (10) ◽  
Author(s):  
Haotian Liu ◽  
Junji Jia
Keyword(s):  
Black Hole ◽  
Time Delay ◽  
Gravitational Lensing ◽  
Angular Position ◽  
Weak Field ◽  
Weak Field Limit ◽  
Perturbative Method ◽  
Total Travel Time ◽  
Sgr A ◽  
The Impact

AbstractTotal travel time t and time delay $$\Delta t$$ Δ t between images of gravitational lensing (GL) in the equatorial plane of stationary axisymmetric (SAS) spacetimes for null and timelike signals with arbitrary velocity are studied. Using a perturbative method in the weak field limit, t in general SAS spacetimes is expressed as a quasi-series of the impact parameter b with coefficients involving the source-lens distance $$r_s$$ r s and lens-detector distances$$r_d$$ r d , signal velocity v, and asymptotic expansion coefficients of the metric functions. The time delay $$\Delta t$$ Δ t to the leading order(s) were shown to be determined by the spacetime mass M, spin angular momentum a and post-Newtonian parameter $$\gamma $$ γ , and kinematic variables $$r_s,~r_d,~v$$ r s , r d , v and source angular position $$\beta $$ β . When $$\beta \ll \sqrt{aM}/r_{s,d}$$ β ≪ aM / r s , d , $$\Delta t$$ Δ t is dominated by the contribution linear to spin a. Modeling the Sgr A* supermassive black hole as a Kerr–Newman black hole, we show that as long as $$\beta \lesssim 1.5\times 10^{-5}$$ β ≲ 1.5 × 10 - 5 [$$^{\prime \prime }$$ ″ ], then $$\Delta t$$ Δ t will be able to reach the $$\mathcal {O}(1)$$ O ( 1 ) second level, which is well within the time resolution of current GRB, gravitational wave and neutrino observatories. Therefore measuring $$\Delta t$$ Δ t in GL of these signals will allow us to constrain the spin of the Sgr A*.

scholarly journals Null geodesics and repulsive behavior of gravity in $(2+1)$D massive gravity

2019 ◽  
Vol 2019 (7) ◽  
Author(s):  
Keisuke Nakashi ◽  
Shinpei Kobayashi ◽  
Shu Ueda ◽  
Hiromi Saida
Keyword(s):  
Black Hole ◽  
Deflection Angle ◽  
Null Geodesic ◽  
Analytic Solutions ◽  
Massive Gravity ◽  
Geodesic Equation ◽  
Null Geodesics ◽  
Black Hole Background ◽  
Black Hole Spacetime ◽  
The Impact

Abstract We study the null geodesics in a static circularly symmetric (SCS) black hole spacetime, which is a solution in the $(2+1)$D massive gravity proposed by Bergshoeff, Hohm, and Townsend (BHT massive gravity). We obtain analytic solutions for the null geodesic equation in the SCS black hole background and find the explicit form of deflection angles. We see that, for various values of the impact parameter, the deflection angle can be positive, negative, or even zero in this black hole spacetime. The negative deflection angle indicates the repulsive behavior of the gravity that comes from the gravitational hair parameter that is the most characteristic quantity of the BHT massive gravity.

scholarly journals Gravitational lensing by charged black hole in regularized 4D Einstein–Gauss–Bonnet gravity

2020 ◽  
Vol 80 (12) ◽  
Author(s):  
Rahul Kumar ◽  
Shafqat Ul Islam ◽  
Sushant G. Ghosh
Keyword(s):  
Black Holes ◽  
Gravitational Lensing ◽  
Deflection Angle ◽  
Strong Field ◽  
Angular Position ◽  
Angular Separation ◽  
Light Deflection ◽  
Charged Black Holes ◽  
The Deflection Angle ◽  
Sgr A

AbstractAmong the higher curvature gravities, the most extensively studied theory is the so-called Einstein–Gauss–Bonnet (EGB) gravity, whose Lagrangian contains Einstein term with the GB combination of quadratic curvature terms, and the GB term yields nontrivial gravitational dynamics in $$ D\ge 5$$ D ≥ 5 . Recently there has been a surge of interest in regularizing, a $$ D \rightarrow 4 $$ D → 4 limit of, the EGB gravity, and the resulting regularized 4D EGB gravity valid in 4D. We consider gravitational lensing by Charged black holes in the 4D EGB gravity theory to calculate the light deflection coefficients in strong-field limits $$\bar{a}$$ a ¯ and $$\bar{b}$$ b ¯ , while former increases with increasing GB parameter $$\alpha $$ α and charge q, later decrease. We also find a decrease in the deflection angle $$\alpha _D$$ α D , angular position $$\theta _{\infty }$$ θ ∞ decreases more slowly and impact parameter for photon orbits $$u_{m}$$ u m more quickly, but angular separation s increases more rapidly with $$\alpha $$ α and charge q. We compare our results with those for analogous black holes in General Relativity (GR) and also the formalism is applied to discuss the astrophysical consequences in the case of the supermassive black holes Sgr A* and M87*.

Gravitational Lensing by Kerr-Sen Dilaton-Axion Black Hole in the Weak Deflection Limit

2010 ◽  
Author(s):  
G. N. Gyulchev ◽  
S. S. Yazadjiev ◽  
Michail D. Todorov ◽  
Christo I. Christov
Keyword(s):  
Black Hole ◽  
Gravitational Lensing ◽  
Deflection Limit
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