We unveil a novel class of traversable wormholes exhibiting exact spherical symmetry, geometrically inspired by the minimal surface structure of a catenoid. Introducing the spacetime metric, we rigorously derive its fundamental curvature properties, including the Riemann curvature tensor, and consequently compute the Einstein tensor and stress-energy tensor. This framework reveals that the wormhole is sustained by an anisotropic fluid. A detailed analysis of the energy conditions demonstrates the requisite presence of exotic matter, establishing the physical viability and constraints of this configuration. Subsequent investigations address the wormhole’s traversability characteristics, gravitational lensing signatures, and dynamic stability. Crucially, we establish that this catenoid-inspired spacetime represents a finite wormhole, possessing bounded spatial extent.

India

Bikramarka S. Choudhury

Md Khalid Hossain

Farook Rahaman

Catenoid inspired hyperbolic wormhole geometry

Using Newton s stellar balance equation in conjunction with the observed flat rotation velocities of satellite galaxies, we estimate the speed of sound in a dark matter medium. Our analysis reveals that the orbital velocities of these satellite galaxies significantly exceed the calculated sound speed. This disparity implies that the satellites traverse the dark matter medium at supersonic speeds, thereby giving rise to shock waves within it.Our observational study also supports this conclusion by examining nine spiral galaxies, where we consistently find that the inclination-corrected flat rotation velocities ( <math altimg='si1.svg'><msub><mi>V</mi><mrow><mi mathvariant='normal'>flat</mi></mrow></msub></math>) surpass the dark matter sound speeds (cs). This disparity holds across a range of dark matter surface densities, demonstrating that supersonic motion and consequent shock wave generation are robust features in diverse galactic environments.

Mofazzal Azam

M. Sami

Anikul Islam

Aritra Sanyal

Romania

Irina Radinschi

An observation on shock waves in a dark matter medium

In this article, we study the weak gravitational lensing in the background of regular, static, spherically symmetric black hole solutions of Einstein’s standard general relativity coupled with nonlinear electrodynamics. The weak deflection angles are estimated in the context of vacuum medium and plasma medium using the Gauss-Bonnet method. The obtained deflection angles decrease as the impact parameter <math altimg='si6.svg'><mi>b</mi></math> and the charge parameter <math altimg='si9.svg'><mi>q</mi></math> increase, while the deflection angles increase gradually with increasing values of the black hole mass <math altimg='si11.svg'><mi>m</mi></math>. Moreover, the effect of a plasma medium has increased the deflection angle than the vacuum medium scenario. We also estimate the time delay in the field of the described black holes that vanishes for <math altimg='si29.svg'><mrow><mi>m</mi><mo linebreak='goodbreak'>=</mo><mi>q</mi><mo linebreak='goodbreak'>=</mo><mn>0</mn></mrow></math>, i.e., the absence of the black holes. The shadow cast of the present black holes is also analyzed with respect to the impact <math altimg='si9.svg'><mi>q</mi></math> and mass <math altimg='si11.svg'><mi>m</mi></math>, which ensures that the shadow region shrinks for increasing values of <math altimg='si9.svg'><mi>q</mi></math> and expands for increasing values of <math altimg='si11.svg'><mi>m</mi></math>. In addition, we estimated the rigorous bounds of the greybody factor <math altimg='si18.svg'><msub><mi mathvariant='script'>T</mi><mi>b</mi></msub></math> for the described black holes and the graphical analysis ensures that the increasing charge parameter <math altimg='si9.svg'><mi>q</mi></math> decreases the rigorous bound of <math altimg='si18.svg'><msub><mi mathvariant='script'>T</mi><mi>b</mi></msub></math> and the increasing mass <math altimg='si11.svg'><mi>m</mi></math> increases the rigorous bound of <math altimg='si18.svg'><msub><mi mathvariant='script'>T</mi><mi>b</mi></msub></math>.

Susmita Sarkar

Nayan Sarkar

Pakistan

Hasrat Hussian Shah

Pankaj Balo

Deflection angle of regular black holes in nonlinear electrodynamics: Gauss-Bonnet theorem, time delay, shadow, and greybody bound

In this article, accretion of particular dark energy candidates is studied. These dark energy models possess equation of state dependent on redshift and some free parameters. Central gravitating object for this accretion model is chosen to be the Kehagias Sfetsos black hole sitting in Horava Gravity. Four special redshift parametrization models, viz. Chevallier–Polarski–Linder, Jassal–Bagala–Padmanabhan, Barboza–Alcaniz and Barboza–Alcaniz–Zhu–Silva are picked to study different accretion properties. Formation of critical point and related radial infalling speed, sonic speed, different arbitrary parameters’ values etc are obtained. Mass growth curves are plotted. The rate of growth is followed to depend on the dark matter’s behavior as well as the free parameters of dark energy models. Future loss in mass is noted for some of the chosen dark energy models.

Promila Biswas

Sukanya Dutta

Ritabrata Bisawas

Accretion of dark energy candidates following redshift parametrization type equation of state: Horava–Lifshitz gravity

A shear-free, collapsing compact object, described by an embedding class I solution and emitting radiation, is presented here. Because of the properties of embedding class I, this four-dimensional interior spacetime can be embedded in pseudo-flat five-dimensional space. Starting with an initially static and shear-free gravitating body through the Karmarkar condition, we have explored the time evolution of the system using the time-dependent Einstein field equations. The interior solution is smoothly matched with the Vaidya outgoing solution across a time-like hypersurface which yields the temporal behaviour of the model. Further, a thorough physical analysis of the thermodynamic variables has been presented spatially and temporally. As the time progresses into the future, the surface compactness factor approaches the Buchdahl limit until it crosses this to proceed with the collapse. Before  $$2m_\Sigma /r_\Sigma \rightarrow 8/9$$  <math> <mrow> <mn>2</mn> <msub> <mi>m</mi> <mi>Σ</mi> </msub> <mo>/</mo> <msub> <mi>r</mi> <mi>Σ</mi> </msub> <mo>→</mo> <mn>8</mn> <mo>/</mo> <mn>9</mn> </mrow> </math>  , the equation of state adjusts itself like a self-immune system to hold the system by increasing  $$\Gamma _{rc}$$  <math> <msub> <mi>Γ</mi> <mrow> <mi>rc</mi> </mrow> </msub> </math>   (i.e. increasing stiffness). All the physical quantities, e.g., density, pressure anisotropy, radiation, luminosity, temperature, are non-singular throughout the interior of the star at a finite time slice. As the time progresses, these quantities point towards a future singularity. Throughout the evolution, the surface density and surface pressure always remain lower than their corresponding central values. Similarly, the causal temperature also always remains higher than the non-causal counterpart throughout the interior as well as during the evolution.

Ksh. Singh

Bidisha Samanta

Oman

S. Maurya

N. Singh

Anil Aria

Shear-free collapsing compact star in pseudo-flat 5-D spacetime emitting radiation

We study wormhole as the solution of the Wheeler–DeWitt (WdW) equation satisfying Hawking–Page wormhole boundary conditions in Friedmann–Robertson–Walker (FRW) cosmology. The quantum wormholes are formulated with arbitrary factor ordering of the Hamiltonian constraint operators with perfect fluid matter sources as well as minimally coupled scalar fields.

Bikramarka Choudhury

Euclidean quantum wormholes

Spacetime singularity is not observed directly as it is covered by event horizon. Naked singularities may be formed due to gravitational collapse without an event horizon. Therefore, cosmic censorship conjecture entails advanced ascertainment. Recently, Joshi et al. have discovered a naked singularity solution (known as JMN naked singularity), which emerges from the dynamical gravitational collapse of a massive matter cloud. Since several studies are needed to know more extra characteristics that may help to test cosmic censorship conjecture in general relativity, therefore, we thought it is pertinent to study the deflection of massive particles by the naked singularity. We shall examine massive particles paths and deflection angles near naked singularities in this research. To get the deflection angle, we employ the Gauss-Bonet technique and the Rindler-Ishak method. The results of the two procedures are compared in detail.

Japan

Keita Takizawa

Shyam Das

Gravitational deflection of massive body around naked singularity

In this paper, we obtain analytical solutions of Einstein field equations for a spherically symmetric anisotropic matter distributions. For this purpose physically meaningful metric potential corresponds to  $$g_{rr}$$  <math> <msub> <mi>g</mi> <mrow> <mi>rr</mi> </mrow> </msub> </math>   and a particular choice of the anisotropy has been utilized to obtain the solutions in closed form. This class of solution has been used to characterized observed pulsars from different aspects. Smooth matching of interior spacetime metric with the exterior Schwarzschild metric and in addition with the condition of vanishing radial pressure across the boundary leads us to determine the model parameters. Pulsar  $$4U1820-30$$  <math> <mrow> <mn>4</mn> <mi>U</mi> <mn>1820</mn> <mo>-</mo> <mn>30</mn> </mrow> </math>   with its current estimated data for mass and radius (Mass  $$=1.58 M_\odot $$  <math> <mrow> <mo>=</mo> <mn>1.58</mn> <msub> <mi>M</mi> <mo>⊙</mo> </msub> </mrow> </math>   and radius  $$=9.1$$  <math> <mrow> <mo>=</mo> <mn>9.1</mn> </mrow> </math>   km) has been allowed for testing the physical acceptability of our developed model. We have graphically analyzed the gross physical features of the observed pulsar. The stability of the model is also discussed under the conditions of causality, adiabatic index and generalized Tolman–Oppenheimer–Volkov (TOV) equation under the forces acting on the system. Few more pulsars with their have been considered, to show that this model is compatible with observational data, and all the requirements of a realistic star are highlighted. Mass-radius (M–R) relationship have been generated for our model. The impact of anisotropy on the gross physical features of stars have been explored with the graphical presentation.

Koushik Chakraborty

Shreya Majumder

Study of compact objects: a new analytical stellar model

We analyse traversable wormholes defined by the dynamic line elements that asymptotically approach Friedmann–Robertson–Walker (FRW) universe. These dynamical wormholes is supported by the galactic dark matter as well as perfect isotropic fluid. We will discuss several evolving Lorentzian wormholes comprising with different perfect isotropic fluids in addition to various scale factors. We will speculate the various significance, features and throat energy conditions for these evolving traversable Lorentzian wormholes.

Evolving wormhole geometry from dark matter energy density

In this article, we apply the Finsler spacetime to develop the Einstein field equations in the extension of modified geometry. Following Finsler geometry, which is focused on the tangent bundle with a scalar function, a scalar equation should be the field equation that defines this structure. This spacetime maintains the required causality properties on the generalized Lorentzian metric manifold. The matter field is coupled with the Finsler geometry to produce the complete action. The developed Einstein field equations are employed on the strange stellar system to improve the study. The interior of the system is composed of a strange quark matter, maintained by the MIT bag equation of state. In addition, the modified Tolman–Oppenheimer–Volkov (TOV) equation is formulated. In particular, the anisotropic stress attains the maximum at the surface. The mass-central density variation confirms the stability of the system.

Sourav Chowdhury

Debabrata Deb

Saibal Ray

Finslerian extension of an anisotropic strange star in the domain of modified gravity