Shadows Of Magnetically Charged Rotating Black Holes Surrounded By Quintessence

By employing the very long baseline interferometry technique,the image of M87*was recently captured by the Event Horizon Telescope Collaboration.Besides the achievement of another milestone in observing the spacetime geometry of the strong field region in terms of the electromagnetic signals,it leads to a promising future of astrophysics.Based on the Van Cittert-Zernike theorem,the measurements of the Fourier transform of the brightness distribution were accomplished through the correlated signals between distant observatories.As was first pointed out in the literature by Bardeen et al.,certain optical features of the image,such as the black hole shadow,are entirely governed by the intrinsic black hole parameters,such as the mass,charge,and angular momentum.As a result,they constitute a direct probe of the compact object.On the practical side,however,at the present stage,the obtained image still largely depends on the specified structure of the accretion disk of the black hole,as well as its dynamics.It is expected,as the planetary scale efforts continue,one might eventually acquire images with substantially better resolution,from which the photon rings can be unambiguously identified.Accordingly,on the theoretical side,the studies of black hole shadow have triggered a wave of renewed interest in recent years.The accelerating expansion of our Universe implies that a significant portion of the energy density is dark,namely,in the form of an exotic fluid of negative pressure.On the other hand,astro-observations suggest that 70%of the universe seems to be a uniformly distributed exotic fluid,while 30%seems to be made of protons,neutrons and some weakly interactive particles known as dark matter.Scientists believe,based on the observation of the luminosity distances of a type-Ⅰ supernovae that the current acceleration is an effect of this exotic fluid.Apart from the cosmological constant ∧,other prescriptions of dark energy consist of different dynamic models.Among others,quintessence provides a dynamical description of dark energy in terms of a minimally coupled scalar field.Regarding the equation of state p=ω?,the model’s state parameter ω usually falls within the range of-1≤ω≤-1/3.In particular,the case ω=-1 is reminiscent of that of a constant cosmological constant.The quintessence perturbs the black hole background metric and also modifies the curves of space-time around the singularity.Moreover,cosmological horizons exist in the space-time of black holes or other compact objects immersed in this kind of scalar field.In this thesis,we study the optical properties of a class of magnetically charged rotating black hole spacetimes.Firstly,we briefly discuss the main characteristics of the black hole metric in question.The black holes in question are assumed to be immersed in the quintessential field,and subsequently,the resulting black hole shadows are expected to be modified by the presence of the dark energy.Secondly,we then proceed to analyze the horizon structure and the photon region as a function of the metric parameters.We investigate the photon region and the horizon,and in particular,their dependence on the relevant physical conditions such as the state parameter of the quintessence,the angular momentum,and the magnitude of the magnetic charge.It is shown that the photon regions sensitively depend on the horizon structure and possess intricate features.Moreover,we also study the black hole shadow of the black hole immersed in the quintessential field and the influence of the metric parameters on its structure at the angle of the observer at infinity,and we are interested in exploring the dependence of the BH shadow on the state parameter of dark energy in our study.Finally,from the view of the zero angular momentum observer,we extend the study to possible quantitatively observables,and in particular,those associated with the distortion parameters of the black hole shadow.The variation of these observables with the parameters of the metric essentially reflects the effect on the observed black hole shadows.