Shadow and photon sphere of black hole in clouds of strings and quintessence

In this study,we investigate the shadow and photon sphere of the black bole in clouds of strings and quintessence with static and infalling spherical accretions.We obtain the geodesics of the photons near a black hole with different impact parameters b to investigate how the string cloud model and quintessence influence the specific intensity by altering the geodesic and the average radial position of photons.In addition,the range of the string cloud parameter a is constrained to ensure that a shadow can be observed.Moreover,the light sources in the accretion follow a normal distribution with an attenuation factorγ,and we adopt a model of the photon emissivity j(v_(e))to obtain the specific intensities.Furthermore,the shadow with static spherical accretion is plotted,which demonstrates that the apparent shape of the shadow is a perfect circle,and the value ofγinfluences the brightness of the photon sphere.Subsequently,we investigate the profile and specific intensity of the shadows with static and infalling spherical accretions,respectively.The interior of the shadows with an infalling spherical accretion will be darker than that with the static spherical accretion,and the specific intensity with both static and infalling spherical accretions gradually converges.

Microstructure of charged AdS black hole with minimal length effects

In this work,the microstructure of charged AdS black holes under minimal length effects is investigated.We study the thermodynamics of black holes in the extended phase space,where the cosmological constant is regarded as the thermodynamic pressure.The modified Hawking temperature and phase transition are obtained based on the generalized uncertainty principle(GUP).Then,using thermodynamic geometry,the microstructure of black holes can be determined by the ratio of the GUP parameter to charge.For a small ratio,the black hole exhibits the typical RN-AdS microstructure with van der Waals phase transition and repulsive/attractive interactions.As the ratio increases,the reentrant phase transition is observed,and both the repulsion-attraction coexisted and the attraction dominated black holes are noted.For a large ratio,the black hole behaves like a Schwarzchild-AdS black hole in which neither phase transition nor repulsive interaction are observed.These results suggest that the GUP effect will reduce the repulsive interaction presented by the charged AdS black hole.