We investigate the dynamics of a charged particle being kicked off from its circular orbit around a regular black hole by an incoming massive particle in the presence of magnetic field. The resulting escape velocity, ...We investigate the dynamics of a charged particle being kicked off from its circular orbit around a regular black hole by an incoming massive particle in the presence of magnetic field. The resulting escape velocity, escape energy and the effective potential are analyzed. It is shown that the presence of even a very weak magnetic field helps the charged particles in escaping the gravitational field of the black hole. Moreover the effective force acting on the particle visibly reduces with distance. Thus particle near the black hole will experience higher effective force as compared to when it is far away.展开更多
We derive the first law of thermodynamics using the method proposed by Wald.Treating the entropy as Noether charge and comparing with the usual first law of thermodynamics,we obtain explicitly the expression of entrop...We derive the first law of thermodynamics using the method proposed by Wald.Treating the entropy as Noether charge and comparing with the usual first law of thermodynamics,we obtain explicitly the expression of entropy which contains infinitely many non-local terms(i.e.the integral terms).We have proved,in general,that the first law of black hole thermodynamics is violated for f(R,T)gravity.However,there might exist some special cases in which the first law for f(R,T)gravity is recovered.展开更多
Motivated by an earlier study of Sahoo and Singh[Mod.Phys.Lett.A 17(2002)2409],we investigate the time dependence of the Brans–Dicke parameterω(t)for an expanding Universe in the generalized Brans–Dicke Chameleon c...Motivated by an earlier study of Sahoo and Singh[Mod.Phys.Lett.A 17(2002)2409],we investigate the time dependence of the Brans–Dicke parameterω(t)for an expanding Universe in the generalized Brans–Dicke Chameleon cosmology,and obtain an explicit dependence ofω(t)in different expansion phases of the Universe.Also,we discuss how the observed accelerated expansion of the observable Universe can be accommodated in the present formalism.展开更多
The study of black hole(BH)shadows provides crucial insights into the nature of strong gravitational effects and the intricate structure of spacetime surrounding BHs.In this study,we investigate the shadow of a Kerr M...The study of black hole(BH)shadows provides crucial insights into the nature of strong gravitational effects and the intricate structure of spacetime surrounding BHs.In this study,we investigate the shadow of a Kerr MOG BH in a plasma environment,examining the extent to which the presence of plasma alters the characteristics of the observed shadow compared with that in vacuum conditions.Our analysis reveals that the shadow characteristics of M87*and Sgr A*are more compatible with event horizon telescope(EHT)observational data in nonhomogeneous plasma spacetime than in homogeneous plasma spacetime.For a small metric deformation parameterα,the shadow aligns within 2σuncertainty for homogeneous plasma and within 1σfor nonhomogeneous plasma.Next,we determine the energy emission rate for the Kerr MOG BH and analyze the influence of parametersα,k_(o),k_(θ),and k_(r)on particle emissions in the BH vicinity.We further analyze the deflection angle in the presence of homogeneous and nonhomogeneous plasma profiles.The findings indicate notable differences from the vacuum scenario,underscoring the importance of accounting for plasma effects in examining light propagation around compact objects.展开更多
We study the spin precession frequency of a test gyroscope attached to a stationary observer in the five-dimensional rotating Kaluza-Klein black hole(RKKBH). We derive the conditions under which the test gyroscope mov...We study the spin precession frequency of a test gyroscope attached to a stationary observer in the five-dimensional rotating Kaluza-Klein black hole(RKKBH). We derive the conditions under which the test gyroscope moves along a timelike trajectory in this geometry, and the regions where the spin precession frequency diverges. The magnitude of the gyroscope precession frequency around the KK black hole diverges at two spatial locations outside the event horizon. However, in the static case, the behavior of the Lense-Thirring frequency of a gyroscope around the KK black hole is similar to the ordinary Schwarzschild black hole. Since a rotating Kaluza-Klein black hole is a generalization of the Kerr-Newman black hole, we present two mass-independent schemes to distinguish these two spacetimes.展开更多
In this study,the optical properties of a renormalization group improved(RGI)Schwarzschild black hole(BH)are investigated in a plasma medium.Beginning with the equations of motion in a plasma medium,we aim to present ...In this study,the optical properties of a renormalization group improved(RGI)Schwarzschild black hole(BH)are investigated in a plasma medium.Beginning with the equations of motion in a plasma medium,we aim to present the modifications in the shadow radius of the RGI BH.To this end,we compute the deflection angle of light in the weak gravity regime for uniform and non-uniform plasma media.Importantly,owing to the plasma media,we discover that the equations of motion for light obtained from the radiating and infalling/rest gas have to be modified.This,in turn,changes and modifies the expression for the intensity observed far away from the BH.Finally,we obtain the shadow images for the RGI BH for different plasma models.Although quantum effects change the background geometry,such effects are minimal,and practically detecting these effects using the current technology based on supermassive BH shadows is impossible.The parameterΩencodes the quantum effects,and in principle,one expects such quantum effects to play significant roles only for very small BHs.However,the effects of plasma media can play an important role in the optical appearance of BHs,as they affect and modify the equations of motion.展开更多
The transonic phenomenon of black hole accretion and the existence of the photon sphere characterize strong gravitational fields near a black hole horizon.Here,we study the spherical accretion flow onto general parame...The transonic phenomenon of black hole accretion and the existence of the photon sphere characterize strong gravitational fields near a black hole horizon.Here,we study the spherical accretion flow onto general parametrized spherically symmetric black hole spacetimes.We analyze the accretion process for various perfect fluids,such as the isothermal fluids of ultra-stiff,ultra-relativistic,and sub-relativistic types,and the polytropic fluid.The influences of additional parameters,beyond the Schwarzschild black hole in the framework of general parameterized spherically symmetric black holes,on the flow behavior of the above-mentioned test fluids are studied in detail.In addition,by studying the accretion of the ideal photon gas,we further discuss the correspondence between the sonic radius of the accreting photon gas and the photon sphere for general parameterized spherically symmetric black holes.Possible extensions of our analysis are also discussed.展开更多
One of the major open problems in theoretical physics is the lack of a consistent quantum gravity theory.Recent developments in our knowledge on thermodynamic phase transitions of black holes and their van der Waalsli...One of the major open problems in theoretical physics is the lack of a consistent quantum gravity theory.Recent developments in our knowledge on thermodynamic phase transitions of black holes and their van der Waalslike behavior may provide an interesting quantum interpretation of classical gravity.Studying different methods of investigating phase transitions can extend our understanding of the nature of quantum gravity.In this paper,we present an alternative theoretical approach for finding thermodynamic phase transitions in the extended phase space.Unlike the standard methods based on the usual equation of state involving temperature,our approach uses a new quasiequation constructed from the slope of temperature versus entropy.This approach addresses some of the shortcomings of the other methods and provides a simple and powerful way of studying the critical behavior of a thermodynamical system.Among the applications of this approach,we emphasize the analytical demonstration of possible phase transition points and the identification of the non-physical range of horizon radii for black holes.展开更多
Asymptotically safe gravity is an effective approach to quantum gravity.It is important to differentiate modified gravity,which is inspired by asymptotically safe gravity.In this study,we examine particle dynamics nea...Asymptotically safe gravity is an effective approach to quantum gravity.It is important to differentiate modified gravity,which is inspired by asymptotically safe gravity.In this study,we examine particle dynamics near the improved version of a Schwarzschild black hole.We assume that in the context of an asymptotically safe gravity scenario,the ambient matter surrounding the black hole is of isothermal nature,and we investigate the spherical accretion of matter by deriving solutions at critical points.The analysis of various values of the state parameter for isothermal test fluids,viz.,k=1,1/2,1/3,1/4 show the possibility of accretion onto an asymptotically safe black hole.We formulate the accretion problem as Hamiltonian dynamical system and explain its phase flow in detail,which reveals interesting results in the asymptotically safe gravity theory.展开更多
文摘We investigate the dynamics of a charged particle being kicked off from its circular orbit around a regular black hole by an incoming massive particle in the presence of magnetic field. The resulting escape velocity, escape energy and the effective potential are analyzed. It is shown that the presence of even a very weak magnetic field helps the charged particles in escaping the gravitational field of the black hole. Moreover the effective force acting on the particle visibly reduces with distance. Thus particle near the black hole will experience higher effective force as compared to when it is far away.
文摘We derive the first law of thermodynamics using the method proposed by Wald.Treating the entropy as Noether charge and comparing with the usual first law of thermodynamics,we obtain explicitly the expression of entropy which contains infinitely many non-local terms(i.e.the integral terms).We have proved,in general,that the first law of black hole thermodynamics is violated for f(R,T)gravity.However,there might exist some special cases in which the first law for f(R,T)gravity is recovered.
文摘Motivated by an earlier study of Sahoo and Singh[Mod.Phys.Lett.A 17(2002)2409],we investigate the time dependence of the Brans–Dicke parameterω(t)for an expanding Universe in the generalized Brans–Dicke Chameleon cosmology,and obtain an explicit dependence ofω(t)in different expansion phases of the Universe.Also,we discuss how the observed accelerated expansion of the observable Universe can be accommodated in the present formalism.
文摘The study of black hole(BH)shadows provides crucial insights into the nature of strong gravitational effects and the intricate structure of spacetime surrounding BHs.In this study,we investigate the shadow of a Kerr MOG BH in a plasma environment,examining the extent to which the presence of plasma alters the characteristics of the observed shadow compared with that in vacuum conditions.Our analysis reveals that the shadow characteristics of M87*and Sgr A*are more compatible with event horizon telescope(EHT)observational data in nonhomogeneous plasma spacetime than in homogeneous plasma spacetime.For a small metric deformation parameterα,the shadow aligns within 2σuncertainty for homogeneous plasma and within 1σfor nonhomogeneous plasma.Next,we determine the energy emission rate for the Kerr MOG BH and analyze the influence of parametersα,k_(o),k_(θ),and k_(r)on particle emissions in the BH vicinity.We further analyze the deflection angle in the presence of homogeneous and nonhomogeneous plasma profiles.The findings indicate notable differences from the vacuum scenario,underscoring the importance of accounting for plasma effects in examining light propagation around compact objects.
文摘We study the spin precession frequency of a test gyroscope attached to a stationary observer in the five-dimensional rotating Kaluza-Klein black hole(RKKBH). We derive the conditions under which the test gyroscope moves along a timelike trajectory in this geometry, and the regions where the spin precession frequency diverges. The magnitude of the gyroscope precession frequency around the KK black hole diverges at two spatial locations outside the event horizon. However, in the static case, the behavior of the Lense-Thirring frequency of a gyroscope around the KK black hole is similar to the ordinary Schwarzschild black hole. Since a rotating Kaluza-Klein black hole is a generalization of the Kerr-Newman black hole, we present two mass-independent schemes to distinguish these two spacetimes.
基金supported by the following grants of the Uzbekistan Ministry for Innovative Development:Research Grant(FZ-20200929344 and F-FA-2021-510)。
文摘In this study,the optical properties of a renormalization group improved(RGI)Schwarzschild black hole(BH)are investigated in a plasma medium.Beginning with the equations of motion in a plasma medium,we aim to present the modifications in the shadow radius of the RGI BH.To this end,we compute the deflection angle of light in the weak gravity regime for uniform and non-uniform plasma media.Importantly,owing to the plasma media,we discover that the equations of motion for light obtained from the radiating and infalling/rest gas have to be modified.This,in turn,changes and modifies the expression for the intensity observed far away from the BH.Finally,we obtain the shadow images for the RGI BH for different plasma models.Although quantum effects change the background geometry,such effects are minimal,and practically detecting these effects using the current technology based on supermassive BH shadows is impossible.The parameterΩencodes the quantum effects,and in principle,one expects such quantum effects to play significant roles only for very small BHs.However,the effects of plasma media can play an important role in the optical appearance of BHs,as they affect and modify the equations of motion.
基金C.L.,T.Z.,and Q.W.are supported by National Natural Science Foundation of China(11675143)the Zhejiang Provincial Natural Science Foundation of China(LY20A050002)the Fundamental Research Funds for the Provincial Universities of Zhejiang in China(RF-A2019015)。
文摘The transonic phenomenon of black hole accretion and the existence of the photon sphere characterize strong gravitational fields near a black hole horizon.Here,we study the spherical accretion flow onto general parametrized spherically symmetric black hole spacetimes.We analyze the accretion process for various perfect fluids,such as the isothermal fluids of ultra-stiff,ultra-relativistic,and sub-relativistic types,and the polytropic fluid.The influences of additional parameters,beyond the Schwarzschild black hole in the framework of general parameterized spherically symmetric black holes,on the flow behavior of the above-mentioned test fluids are studied in detail.In addition,by studying the accretion of the ideal photon gas,we further discuss the correspondence between the sonic radius of the accreting photon gas and the photon sphere for general parameterized spherically symmetric black holes.Possible extensions of our analysis are also discussed.
基金supported financially by the Research Institute for Astronomy and Astrophysics of Maragha, Iran
文摘One of the major open problems in theoretical physics is the lack of a consistent quantum gravity theory.Recent developments in our knowledge on thermodynamic phase transitions of black holes and their van der Waalslike behavior may provide an interesting quantum interpretation of classical gravity.Studying different methods of investigating phase transitions can extend our understanding of the nature of quantum gravity.In this paper,we present an alternative theoretical approach for finding thermodynamic phase transitions in the extended phase space.Unlike the standard methods based on the usual equation of state involving temperature,our approach uses a new quasiequation constructed from the slope of temperature versus entropy.This approach addresses some of the shortcomings of the other methods and provides a simple and powerful way of studying the critical behavior of a thermodynamical system.Among the applications of this approach,we emphasize the analytical demonstration of possible phase transition points and the identification of the non-physical range of horizon radii for black holes.
基金Supported in part by Hebei Provincial Natural Science Foundation of China(A2014201068)。
文摘Asymptotically safe gravity is an effective approach to quantum gravity.It is important to differentiate modified gravity,which is inspired by asymptotically safe gravity.In this study,we examine particle dynamics near the improved version of a Schwarzschild black hole.We assume that in the context of an asymptotically safe gravity scenario,the ambient matter surrounding the black hole is of isothermal nature,and we investigate the spherical accretion of matter by deriving solutions at critical points.The analysis of various values of the state parameter for isothermal test fluids,viz.,k=1,1/2,1/3,1/4 show the possibility of accretion onto an asymptotically safe black hole.We formulate the accretion problem as Hamiltonian dynamical system and explain its phase flow in detail,which reveals interesting results in the asymptotically safe gravity theory.
