In weak field limits,we compute the deflection angle of a gravitational decoupling extended black hole(BH)solution.We obtained the Gaussian optical curvature by examining the null geodesic equations with the help of G...In weak field limits,we compute the deflection angle of a gravitational decoupling extended black hole(BH)solution.We obtained the Gaussian optical curvature by examining the null geodesic equations with the help of Gauss-Bonnet theorem(GBT).We also looked into the deflection angle of light by a black hole in weak field limits with the use of the Gibbons-Werner method.We verify the graphical behavior of the black hole after determining the deflection angle of light.Additionally,in the presence of the plasma medium,we also determine the deflection angle of the light and examine its graphical behavior.Furthermore,we compute the Einstein ring via gravitational decoupling extended black hole solution.We also compute the quasi-periodic oscillations and discuss their graphical behavior.展开更多
Verlinde's emergent gravity(VEG)posits that gravity arises as an emergent phenomenon rooted in the entropic properties of spacetime,challenging the traditional view of gravity as a fundamental force.Building on th...Verlinde's emergent gravity(VEG)posits that gravity arises as an emergent phenomenon rooted in the entropic properties of spacetime,challenging the traditional view of gravity as a fundamental force.Building on this paradigm,recent developments have introduced a novel class of black holes within the VEG framework,revealing intriguing connections between apparent dark matter effects and the distribution of baryonic matter.In this study,we delve into the observational signatures of a Simpson–Visser(SV)Minkowski core regular black hole in VEG,focusing on its shadow images and intensity profiles.Our analysis highlights the profound influence of model parameters,including A(governing baryonic matter distribution),B(strength of interaction between apparent dark matter and baryonic matter),and n(characterizing diverse spacetime geometries),on the effective potential and observable properties.Notably,we find that the modifications introduced by these parameters lead to distinct changes in the black hole's shadow size and intensity distribution.Comparing our results to the Reissner–Nordström(RN)black hole,we uncover a striking reduction in the apparent shadow size and an enhancement in intensity for the SV solution in VEG.展开更多
The current sheath velocity in 0.25 Torr gas pressure of Filippov type plasma focus is studied experimentally. By using two tridimensional magnetic probes on top of the anode surface, the current sheath velocity is me...The current sheath velocity in 0.25 Torr gas pressure of Filippov type plasma focus is studied experimentally. By using two tridimensional magnetic probes on top of the anode surface, the current sheath velocity is measured for argon, oxygen and nitrogen. Additionally, the effect of charging voltage on the current sheath velocity is studied in both axial and radial phases. We found that, the maximum current sheath velocities at both radial and axial phases are respectively 4.33 ± 0.28 （cm/μs） and 3.92 ± 0.75 （cm/μs） with argon as the working gas at 17 kV. Also, the minimum values of current sheath velocity are 1.48 ± 0.15 （cm/μs） at the radial phase and 1.14 ± 0.09 （cm/μs） at the axial phase with oxygen at 12 kV. The current sheath velocity at the radial phase is higher than that at the axial phase for all gases and voltages. In this study, variation of the full width half maximum （FWHM） of magnetic probe signals with voltage is investigated for different gases at radial and axial phases.展开更多
As a dedicated solar radioheliograph,the MingantU SpEctral RadioHeliograph(MUSER)has a maximum baseline of more than 3000 m and a frequency range of 400 MHz–15 GHz.According to the classical radio interferometry theo...As a dedicated solar radioheliograph,the MingantU SpEctral RadioHeliograph(MUSER)has a maximum baseline of more than 3000 m and a frequency range of 400 MHz–15 GHz.According to the classical radio interferometry theory,the non-coplanar baseline effect(i.e.,w-term effect)would be considered and calibrated for such a radio instrument.However,little previous literature made the qualitative or quantitative analyses on w-term effects of solar radioheliograph in-depth.This study proposes a complete quantitative analysis of w-term effects for the MUSER.After a brief introduction of the MUSER,we systematically investigate the baseline variations over a year and analyze the corresponding variations of w-term.We further studied the effects of the w-term in the imaging for the specified extended source,i.e.,the Sun.We discussed the possible effects of the w-term,such as image distortion and so on.The simulated results show that the w-term is an essential and unavoidable issue for solar radio imaging with high spatial resolution.展开更多
This paper explores the dynamical feature of Hayward-Letelier black holes in AdS spacetime,emphasizing the effects of the Hayward parameter g,mass M,cosmological constant L,and modification parameterαon their geometr...This paper explores the dynamical feature of Hayward-Letelier black holes in AdS spacetime,emphasizing the effects of the Hayward parameter g,mass M,cosmological constant L,and modification parameterαon their geometry,thermodynamics,and observational features.By utilizing an effective potential method,we investigate the paths of particles,innermost stable circular orbit,and behavior of photon spheres,which connects them to the appearance of black hole shadows.Thermodynamic features such as Hawking temperature and entropy are studied for investigating the effect of L and thermal fluctuations on the stability of black holes.These discoveries connect theoretical ideas with observational astrophysics,which enhances our comprehension of ordinary black holes in AdS models.In this study,we analytically compute the greybody factor for a massless scalar field propagating in the vicinity of a black hole under the assumption of weak coupling to gravity.We investigate the behavior of the effective potential concerning the black hole's mass and charge,revealing that it reaches its maximum at lower values of the cloud of strings parameter.Our results indicate that the radial absorption rate of the scalar field exhibits significant fluctuations,which is influenced by the charge of the black hole and clouds of string,with implications for the dynamics of scalar fields in strong gravitational fields.展开更多
We investigate the optical properties of the spacetime surrounding a Sen black hole,focusing on the black hole shadow,weak gravitational lensing,and time delay effects.Our analysis reveals that the effective charge of...We investigate the optical properties of the spacetime surrounding a Sen black hole,focusing on the black hole shadow,weak gravitational lensing,and time delay effects.Our analysis reveals that the effective charge of the Sen black hole significantly influences these phenomena.Specifically,an increase in the effective charge leads to a decrease in the radius of the photon sphere and a corresponding decrease in the size of the black hole shadow.Additionally,the bending angle of light rays diminishes as the effective charge increases.Our study provides observational bounds on the effective charge based on these optical characteristics.We also examine the magnification of source brightness using the lens equation and analyze the time delay of light in the presence of a surrounding plasma medium.Our findings offer new insights into the impact of effective charge and plasma on the observational signatures of Sen black holes.展开更多
The integrated spectrum of discrete X-ray sources (mainly the active galactic nuclei, AGN) is inconsistent with the observed spectrum of cosmic X-ray background (CXB), and it is so called CXB spectral paradox. The med...The integrated spectrum of discrete X-ray sources (mainly the active galactic nuclei, AGN) is inconsistent with the observed spectrum of cosmic X-ray background (CXB), and it is so called CXB spectral paradox. The medium X-ray spectra of 68 AGNs are adopted, the evolution function of X-ray spectral indices is analyzed statistically, the fraction of CXB is calculated due to AGNs X-ray emission, which shows that almost 100% CXB comes from AGNs X-ray emission. Especially, the integrated spectrum in 2-10 keV is consistent with the observed spectrum of CXB. The spectral paradox of CXB can be interpreted by this result.展开更多
We consider the recently developed black hole in massive Einstein-dilaton gravity including the coupling of the dilaton scalar field to massive graviton terms.This model has different horizon structures such as event ...We consider the recently developed black hole in massive Einstein-dilaton gravity including the coupling of the dilaton scalar field to massive graviton terms.This model has different horizon structures such as event horizons and inner horizons depending on the values of certain parameters.These variations influence how the black hole interacts with its surroundings.We utilize the well-known Novikov-Thorne model to investigate the thin accretion disks into this interesting model.Our research shows a crucial correlation between the dynamics of the accretion disk and the parameters of dilatonic black holes in dilaton-massive gravity.We observe that dilaton-massive gravity leads to significant contraction and outward expansion.We offer a detailed analysis of accretion by examining both direct and secondary images at various radial distances and observation angles.展开更多
Theories on the nucleosynthesis in the very early universe show that the baryonic matter is just a fraction of the cosmic matter. Moreover, the flatness of the space geometry of the universe shows that the cosmic dens...Theories on the nucleosynthesis in the very early universe show that the baryonic matter is just a fraction of the cosmic matter. Moreover, the flatness of the space geometry of the universe shows that the cosmic density factor Ω= 1, this means that most of the cosmic matter exists in the form of dark matter. Confirmed by experiments up to the present, neutrino展开更多
基金funded by the National Natural Science Foundation of China under Grant No.11975145。
文摘In weak field limits,we compute the deflection angle of a gravitational decoupling extended black hole(BH)solution.We obtained the Gaussian optical curvature by examining the null geodesic equations with the help of Gauss-Bonnet theorem(GBT).We also looked into the deflection angle of light by a black hole in weak field limits with the use of the Gibbons-Werner method.We verify the graphical behavior of the black hole after determining the deflection angle of light.Additionally,in the presence of the plasma medium,we also determine the deflection angle of the light and examine its graphical behavior.Furthermore,we compute the Einstein ring via gravitational decoupling extended black hole solution.We also compute the quasi-periodic oscillations and discuss their graphical behavior.
基金the Deanship of Research and Graduate Studies at King Khalid University for funding this work through Large Research Project under grant number RGP2/333/46。
文摘Verlinde's emergent gravity(VEG)posits that gravity arises as an emergent phenomenon rooted in the entropic properties of spacetime,challenging the traditional view of gravity as a fundamental force.Building on this paradigm,recent developments have introduced a novel class of black holes within the VEG framework,revealing intriguing connections between apparent dark matter effects and the distribution of baryonic matter.In this study,we delve into the observational signatures of a Simpson–Visser(SV)Minkowski core regular black hole in VEG,focusing on its shadow images and intensity profiles.Our analysis highlights the profound influence of model parameters,including A(governing baryonic matter distribution),B(strength of interaction between apparent dark matter and baryonic matter),and n(characterizing diverse spacetime geometries),on the effective potential and observable properties.Notably,we find that the modifications introduced by these parameters lead to distinct changes in the black hole's shadow size and intensity distribution.Comparing our results to the Reissner–Nordström(RN)black hole,we uncover a striking reduction in the apparent shadow size and an enhancement in intensity for the SV solution in VEG.
文摘The current sheath velocity in 0.25 Torr gas pressure of Filippov type plasma focus is studied experimentally. By using two tridimensional magnetic probes on top of the anode surface, the current sheath velocity is measured for argon, oxygen and nitrogen. Additionally, the effect of charging voltage on the current sheath velocity is studied in both axial and radial phases. We found that, the maximum current sheath velocities at both radial and axial phases are respectively 4.33 ± 0.28 （cm/μs） and 3.92 ± 0.75 （cm/μs） with argon as the working gas at 17 kV. Also, the minimum values of current sheath velocity are 1.48 ± 0.15 （cm/μs） at the radial phase and 1.14 ± 0.09 （cm/μs） at the axial phase with oxygen at 12 kV. The current sheath velocity at the radial phase is higher than that at the axial phase for all gases and voltages. In this study, variation of the full width half maximum （FWHM） of magnetic probe signals with voltage is investigated for different gases at radial and axial phases.
基金supported by the National SKA Program of China(2020SKA0110300)the Joint Research Fund in Astronomy(U1831204 and U1931141)+3 种基金the National Natural Science Foundation of China(NSFC)the Chinese Academy of Sciences(CAS)the Funds for International Cooperation and Exchange of the NSFC(11961141001)the NSFC(Grant No.11903009)。
文摘As a dedicated solar radioheliograph,the MingantU SpEctral RadioHeliograph(MUSER)has a maximum baseline of more than 3000 m and a frequency range of 400 MHz–15 GHz.According to the classical radio interferometry theory,the non-coplanar baseline effect(i.e.,w-term effect)would be considered and calibrated for such a radio instrument.However,little previous literature made the qualitative or quantitative analyses on w-term effects of solar radioheliograph in-depth.This study proposes a complete quantitative analysis of w-term effects for the MUSER.After a brief introduction of the MUSER,we systematically investigate the baseline variations over a year and analyze the corresponding variations of w-term.We further studied the effects of the w-term in the imaging for the specified extended source,i.e.,the Sun.We discussed the possible effects of the w-term,such as image distortion and so on.The simulated results show that the w-term is an essential and unavoidable issue for solar radio imaging with high spatial resolution.
基金Supported by the Ongoing Research Funding Program,(ORF-2025-650),King Saud University,Riyadh,Saudi Arabia.
文摘This paper explores the dynamical feature of Hayward-Letelier black holes in AdS spacetime,emphasizing the effects of the Hayward parameter g,mass M,cosmological constant L,and modification parameterαon their geometry,thermodynamics,and observational features.By utilizing an effective potential method,we investigate the paths of particles,innermost stable circular orbit,and behavior of photon spheres,which connects them to the appearance of black hole shadows.Thermodynamic features such as Hawking temperature and entropy are studied for investigating the effect of L and thermal fluctuations on the stability of black holes.These discoveries connect theoretical ideas with observational astrophysics,which enhances our comprehension of ordinary black holes in AdS models.In this study,we analytically compute the greybody factor for a massless scalar field propagating in the vicinity of a black hole under the assumption of weak coupling to gravity.We investigate the behavior of the effective potential concerning the black hole's mass and charge,revealing that it reaches its maximum at lower values of the cloud of strings parameter.Our results indicate that the radial absorption rate of the scalar field exhibits significant fluctuations,which is influenced by the charge of the black hole and clouds of string,with implications for the dynamics of scalar fields in strong gravitational fields.
基金partly supported by Research(FZ-20200929344,F-FA-2021-510)of the Uzbekistan Ministry for Innovative DevelopmentSERB-DST for project(CRG/2021/005771)。
文摘We investigate the optical properties of the spacetime surrounding a Sen black hole,focusing on the black hole shadow,weak gravitational lensing,and time delay effects.Our analysis reveals that the effective charge of the Sen black hole significantly influences these phenomena.Specifically,an increase in the effective charge leads to a decrease in the radius of the photon sphere and a corresponding decrease in the size of the black hole shadow.Additionally,the bending angle of light rays diminishes as the effective charge increases.Our study provides observational bounds on the effective charge based on these optical characteristics.We also examine the magnification of source brightness using the lens equation and analyze the time delay of light in the presence of a surrounding plasma medium.Our findings offer new insights into the impact of effective charge and plasma on the observational signatures of Sen black holes.
文摘The integrated spectrum of discrete X-ray sources (mainly the active galactic nuclei, AGN) is inconsistent with the observed spectrum of cosmic X-ray background (CXB), and it is so called CXB spectral paradox. The medium X-ray spectra of 68 AGNs are adopted, the evolution function of X-ray spectral indices is analyzed statistically, the fraction of CXB is calculated due to AGNs X-ray emission, which shows that almost 100% CXB comes from AGNs X-ray emission. Especially, the integrated spectrum in 2-10 keV is consistent with the observed spectrum of CXB. The spectral paradox of CXB can be interpreted by this result.
基金The authors extend their appreciation to the Deanship of Scientific Research at Northern Border University,Arar,KSA for funding this research work through the project number NBU-FFR-2025-1102-06.
文摘We consider the recently developed black hole in massive Einstein-dilaton gravity including the coupling of the dilaton scalar field to massive graviton terms.This model has different horizon structures such as event horizons and inner horizons depending on the values of certain parameters.These variations influence how the black hole interacts with its surroundings.We utilize the well-known Novikov-Thorne model to investigate the thin accretion disks into this interesting model.Our research shows a crucial correlation between the dynamics of the accretion disk and the parameters of dilatonic black holes in dilaton-massive gravity.We observe that dilaton-massive gravity leads to significant contraction and outward expansion.We offer a detailed analysis of accretion by examining both direct and secondary images at various radial distances and observation angles.
基金Project supported by the National Natural Science Foundation of China.
文摘Theories on the nucleosynthesis in the very early universe show that the baryonic matter is just a fraction of the cosmic matter. Moreover, the flatness of the space geometry of the universe shows that the cosmic density factor Ω= 1, this means that most of the cosmic matter exists in the form of dark matter. Confirmed by experiments up to the present, neutrino
