Photon spheres play a pivotal role in the imaging of luminous objects near black holes.In this paper,we examine observational appearances of a star freely falling in hairy black holes,which can possess one or two phot...Photon spheres play a pivotal role in the imaging of luminous objects near black holes.In this paper,we examine observational appearances of a star freely falling in hairy black holes,which can possess one or two photon spheres outside the event horizon.When there exists a single photon sphere,the total luminosity measured by distant observers decreases exponentially with time at late times.Due to successive arrivals of photons orbiting around the photon sphere different times,a specific observer would see a series of light flashes with decreasing intensity,which share a similar frequency content.Whereas in the case with two photon spheres,photons temporarily trapped between the photon spheres can cause a peak of the total luminosity,which is followed by a slow exponential decay,at late times.In addition,these photons lead to one more series of light flashes seen by the specific observer.展开更多
By throwing a test charged particle into a Reissner-Nordstrom(RN)black hole,we test the validity of the first and second laws of thermodynamics and the weak cosmic censorship conjecture(WCCC)with two types of boundary...By throwing a test charged particle into a Reissner-Nordstrom(RN)black hole,we test the validity of the first and second laws of thermodynamics and the weak cosmic censorship conjecture(WCCC)with two types of boundary conditions:the asymptotically anti-de Sitter(AdS)space and a Dirichlet cavity wall placed in an asymptot-ically flat space.For the RN-AdS black hole,the second law of thermodynamics is satisfied,and the WCCC is viol-ated for both extremal and near-extremal black holes.For the RN black hole in a cavity,the entropy can either in-crease or decrease depending on the change in the charge,and the WCCC is satisfied/violated for the extremal/near-extremal black hole.Our results indicate that there may be a connection between the black hole thermodynamics and the boundary condition imposed on the black hole.展开更多
It has been shown that the Christodoulou version of the strong cosmic censorship(SCC)conjecture can be violated for a scalar field in a near-extremal Reissner-Nordstrom-de Sitter black hole.In this paper,we investigat...It has been shown that the Christodoulou version of the strong cosmic censorship(SCC)conjecture can be violated for a scalar field in a near-extremal Reissner-Nordstrom-de Sitter black hole.In this paper,we investigate the effects of higher derivative corrections to the Einstein-Hilbert action on the validity of SCC,by considering a neutral massless scalar perturbation in 5 -and 6 -dimensional Einstein-Maxwell-Gauss-Bonnet-de Sitter black holes.Our numerical results show that the higher derivative term plays a different role in the d=5 case than it does in the d=6 case.For d=5 ,the SCC violation region increases as the strength of the higher derivative term increases.For d=6 ,the SCC violation region first increases and then decreases as the higher derivative correction becomes stronger,and SCC can always be restored for a black hole with a fixed charge ratio when the higher derivative correction is strong enough.Finally,we find that the C^(2) version of SCC is respected in the d=6 case,but can be violated in some near-extremal regimes in the d=5 case.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12105191,11947225,and 11875196)supported by the International Visiting Program for Excellent Young Scholars of Sichuan University。
文摘Photon spheres play a pivotal role in the imaging of luminous objects near black holes.In this paper,we examine observational appearances of a star freely falling in hairy black holes,which can possess one or two photon spheres outside the event horizon.When there exists a single photon sphere,the total luminosity measured by distant observers decreases exponentially with time at late times.Due to successive arrivals of photons orbiting around the photon sphere different times,a specific observer would see a series of light flashes with decreasing intensity,which share a similar frequency content.Whereas in the case with two photon spheres,photons temporarily trapped between the photon spheres can cause a peak of the total luminosity,which is followed by a slow exponential decay,at late times.In addition,these photons lead to one more series of light flashes seen by the specific observer.
基金National Natural Science Foundation of China(11875196,11375121,11005016)。
文摘By throwing a test charged particle into a Reissner-Nordstrom(RN)black hole,we test the validity of the first and second laws of thermodynamics and the weak cosmic censorship conjecture(WCCC)with two types of boundary conditions:the asymptotically anti-de Sitter(AdS)space and a Dirichlet cavity wall placed in an asymptot-ically flat space.For the RN-AdS black hole,the second law of thermodynamics is satisfied,and the WCCC is viol-ated for both extremal and near-extremal black holes.For the RN black hole in a cavity,the entropy can either in-crease or decrease depending on the change in the charge,and the WCCC is satisfied/violated for the extremal/near-extremal black hole.Our results indicate that there may be a connection between the black hole thermodynamics and the boundary condition imposed on the black hole.
基金This work is supported in part by NSF C(11005016,11875196,11375121)。
文摘It has been shown that the Christodoulou version of the strong cosmic censorship(SCC)conjecture can be violated for a scalar field in a near-extremal Reissner-Nordstrom-de Sitter black hole.In this paper,we investigate the effects of higher derivative corrections to the Einstein-Hilbert action on the validity of SCC,by considering a neutral massless scalar perturbation in 5 -and 6 -dimensional Einstein-Maxwell-Gauss-Bonnet-de Sitter black holes.Our numerical results show that the higher derivative term plays a different role in the d=5 case than it does in the d=6 case.For d=5 ,the SCC violation region increases as the strength of the higher derivative term increases.For d=6 ,the SCC violation region first increases and then decreases as the higher derivative correction becomes stronger,and SCC can always be restored for a black hole with a fixed charge ratio when the higher derivative correction is strong enough.Finally,we find that the C^(2) version of SCC is respected in the d=6 case,but can be violated in some near-extremal regimes in the d=5 case.
