scholarly journals Time delay of photons coupled to Weyl tensor in a regular phantom black hole

2020 ◽  
Vol 80 (7) ◽  
Author(s):  
Xu Lu ◽  
Yi Xie
Keyword(s):  
Black Hole ◽  
Time Delay ◽  
Gravitational Lensing ◽  
Weyl Tensor ◽  
Maxwell Theory ◽  
Time Signals

Abstract Time delay of the photons coupled to the Weyl tensor in a regular phantom black hole is investigated in both weak and strong deflection gravitational lensing. We find that the time delay in the weak deflection lensing strongly depends on the phantom hair while the delay in the strong deflection lensing is significantly affected by the hair and the strength of the coupling. We suggest that it is necessary to measure these two kind of time signals for fully understanding and distinguishing such an interaction beyond the standard Einstein–Maxwell theory.

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 Effect of the Hair on Deflection Angle by Asymptotically Flat Black Holes in Einstein-Maxwell-Dilaton Theory

2019 ◽  
Author(s):  
Wajiha Javed ◽  
Jameela Abbas ◽  
Ali Övgün
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Lensing ◽  
Deflection Angle ◽  
Maxwell Theory ◽  
Weak Gravitational Lensing ◽  
Asymptotically Flat ◽  
The Deflection Angle ◽  
The Impact ◽  
Hairy Black Hole

In this paper, we are interested in a model of exact asymptotically flat charged hairy black holes in the background of dilaton potential. We study the weak gravitational lensing in the spacetime of hairy black hole in Einstein-Maxwell theory with a non-minimally coupled dilaton and its non-trivial potential. In doing so, we use the optical geometry of the flat charged hairy black hole for some range of parameter $\gamma$. For this purpose, by using Gauss-Bonnet theorem, we obtain the deflection angle of photon in a spherically symmetric and asymptotically flat spacetime. Moreover, we also investigate the impact of plasma medium on weak gravitational lensing by asymptotically flat charged hairy black hole with a  dilaton potential. Our analytically analyses show the effect of the hair on the deflection angle in weak field limits.

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