arXiv subjects

Saibal Ray

Publications and source records attributed to Saibal Ray.

At least 127 records · Page 7Linked to original sources

arXiv2014

About influence of gravity on heat conductivity process of the Planets

In the present study it is shown that the interaction of a quasi-static gravitational wave through density fluctuations gives rise to a heat conductivity coefficient and hence temperature. This fact is a very important characteristics to establish a heat equilibrium process of such massive body as the Earth and other Planets. To carry out this exercise general mechanism has been provided, which makes a bridge between classical physics and quantum theory, and specific dependence of heat conductivity coefficient in wide region is also calculated.

physics.gen-ph↗

arXiv2014

The higher dimensional gravastars

A new model of gravastar is obtained in $D$-dimensional Einstein gravity. This class of solutions includes the gravastar as an alternative to D-dimensional versions of the Schwarzschild-Tangherlini black hole. The configuration of this new gravastar consists of three different regions with different equations of state: [I] Interior: 0 \leq r < r_1, ρ= -p; [II] Shell: r_1 \leq r < r_2, ρ= p; [III] Exterior: r_2 < r, ρ= p =0. The outer region of this gravastar corresponds to a higher dimensional Schwarzschild-Tangherlini black hole.

physics.gen-ph↗

arXiv2014

Static Charged Fluid in (2+1)-Dimensions Admitting Conformal Killing Vectors

New solutions for $(2+1)$-dimensional Einstein-Maxwell space-time are found for a static spherically symmetric charged fluid distribution with the additional condition of allowing conformal killing vectors (CKV). We discuss physical properties of the fluid parameters. Moreover, it is shown that the model actually represents two structures, namely (i) Gravastar as an alternative of black hole and (ii) Electromagnetic Mass model depending on the nature of the equation state of the fluid. Here the gravitational mass originates from electromagnetic field alone. The solutions are matched with the exterior region of the Ba$\tilde{n}$ados-Teitelboim-Zanelli (BTZ) type isotropic static charged black hole as a consequence of junction conditions. We have shown that the central charge density is dependent on the value of $M_0$, the conserved mass of the BTZ black hole. This in turn depends on the black hole event horizon which again is related to the Hawking radiation temperature of a BTZ black hole. Thus one may have a clue that the central charge density is related with Hawking radiation temperature of the BTZ black hole on the exterior region of the static charged fluid sphere.

gr-qc↗

arXiv2014

Possible existence of wormholes in the galactic halo region

Two observational results, the density profile from simulations performed in the $Λ$CDM scenario and the observed flat galactic rotation curves, are taken as input with the aim of showing that the galactic halo possesses some of the characteristics needed to support traversable wormholes. This result should be sufficient to provide an incentive for scientists to seek observational evidence for wormholes in the galactic halo region.

gr-qc↗

arXiv2014

N.C. Rana: The Life of a `Comet' in the Astrophysical World

Narayan Chandra Rana, a person with extraordinary potential from a remote village of Bengal, India, came into the limelight of the international scientific world through his exceptional talent, zeal and courage. In his very short life-span, he excelled not only into various branches of astrophysics, but also took a leading role in science popularization, text book writing etc. In this paper, life and works of that budding scientist of India have been discussed from multifarious viewpoints.

physics.hist-ph↗

arXiv2013

Scenario of Accelerating Universe from the Phenomenological Λ- Models

Dark matter, the major component of the matter content of the Universe, played a significant role at early stages during structure formation. But at present the Universe is dark energy dominated as well as accelerating. Here, the presence of dark energy has been established by including a time-dependent $Λ$ term in the Einstein's field equations. This model is compatible with the idea of an accelerating Universe so far as the value of the deceleration parameter is concerned. Possibility of a change in sign of the deceleration parameter is also discussed. The impact of considering the speed of light as variable in the field equations has also been investigated by using a well known time-dependent $Λ$ model.

astro-ph↗

arXiv2013

Noncommutative geometry inspired wormholes with conformal motion

This paper discusses a new wormhole solution that admits conformal motion, given a noncommutative-geometry background. After a discussion of the wormhole geometry and the energy conditions, the analysis proceeds with the calculation of the active gravitational mass, a discussion of the TOV equation describing the equilibrium conditions, as well as the nature of the total gravitational energy. The wormhole spacetime is not asymptotically flat and is therefore cut off at some radial distance and joined to an exterior vacuum solution.

physics.gen-ph↗

arXiv2013

Oscillatory Universe, dark energy and general relativity

The concept of oscillatory Universe appears to be realistic and buried in the dynamic dark energy equation of state. We explore its evolutionary history under the frame work of general relativity. We observe that oscillations do not go unnoticed with such an equation of state and that their effects persist later on in cosmic evolution. The `classical' general relativity seems to retain the past history of oscillatory Universe in the form of increasing scale factor as the classical thermodynamics retains this history in the form of increasing cosmological entropy.

physics.gen-ph↗

arXiv2013

Wormholes supported by two non-interacting fluids

We provide a new matter source that supplies fuel to construct wormhole spacetime. The exact wormhole solutions are found in the model having, besides real matter, an anisotropic dark energy. We have shown that the exotic matters that are the necessary ingredients for wormhole physics violate null and weak energy conditions but obey strong energy condition marginally. Though the wormhole comprises of exotic matters yet the effective mass remains positive. We have calculated the effective mass of the wormhole up to 8 km from the throat (assuming throat radius as 4 km) as $1.3559M_\odot $. Some physical features are briefly discussed.

physics.gen-ph↗

arXiv2013

BTZ black holes inspired by noncommutative geometry

In this paper a Banados, Teitelboim and Zanelli (BTZ) black hole is constructed from an exact solution of the Einstein field equations in a (2+1)-dimensional anti-de Sitter spacetime in the context of noncommutative geometry. The BTZ black hole turns out to have two horizons, no horizon or a single horizon corresponding to a minimal mass. Certain thermodynamical properties are investigated, including Hawking temperature, entropy and heat capacity. Also discussed is the geodesic structure of BTZ black holes for both massless and massive particles. In particular, it is shown that bound orbits for test particles are possible.

gr-qc↗

arXiv2012

Central Density Dependent Anisotropic Compact Stars

Stars can be treated as self-gravitating fluid. In this connection, we propose a model for an anisotropic star under the relativistic framework of Krori-Barua (1975) spacetime. It is shown that the solutions are regular and singularity free. The uniqueness of the model is that interior physical properties of the star solely depend on the central density of the matter distribution.

physics.gen-ph↗

arXiv2012

Searching for higher dimensional wormholes with noncommutative geometry

Noncommutative geometry, an offshoot of string theory, replaces point-like structures with smeared objects and has recently been extended to higher dimensions. The purpose of this letter is to obtain wormhole solutions with this extended noncommutative geometry as a background. It is found through this investigation that wormhole solutions exist in the usual four, as well as in five dimensions, but they do not exist in higher-dimensional spacetimes.

gr-qc↗

arXiv2012

Anisotropic Compact stars with variable cosmological constant

Recently the small value of the cosmological constant and its ability to accelerate the expansion of the Universe is of great interest. We discuss the possibility of forming of anisotropic compact stars from this cosmological constant as one of the competent candidates of dark energy. For this purpose we consider the analytical solution of Krori and Barua metric. We take the radial dependence of cosmological constant and check all the regularity conditions, TOV equations, stability and surface redshift of the compact stars. It has been shown as conclusion that this model is valid for any compact star and we have cited $4U 1820-30$ as a specific example of that kind of star.

gr-qc↗

arXiv2012

Anisotropic strange star with de Sitter spacetime

Stars can be treated as self-gravitating fluid. Krori and Barua (1975) gave an analytical solutions to that kind of fluids. In this connection, we propose a de-Sitter model for an anisotropic strange star with the Krori-Barua spacetime. We incorporate the existence of cosmological constant in a small scale to study the structure of anisotropic strange stars and come to conclusion that this doping is very much compatible with the well known physical features of strange stars.

gr-qc↗

arXiv2012

Indian Amateur Astronomer R. G. Chandra: A unique AAVSO member

In this Note, which is a sequel on the Indian amateur astronomer R.G. Chandra [Biswas2011a, Biswas2011b], we have presented some documents to reveal his three-decades relationship with the American Association for Variable Stars Observers and other connection to American astronomical societies. We have given a short account of his observations on different category, viz. (i) Variable stars, (ii) Nova, (iii) Meteors and (iv) Andromedae. His responsibilities and recognitions are also discussed.

physics.hist-ph↗

arXiv2012

Magnetized dark energy and the late time acceleration

In the present work we have searched the existence of the late time acceleration of the Universe. The matter source that is responsible for the late time acceleration of the Universe consists of cosmic fluid with the equation of state parameter $ω=\frac{p}ρ$ and uniform magnetic field of energy density $ρ_{B}$. The study is done here under the framework of spatially homogeneous and anisotropic locally rotationally symmetric (LRS) Bianchi-I cosmological model in the presence of magnetized dark energy. To get the deterministic model of the Universe, we assume that the shear scalar $(σ)$ in the model is proportional to expansion scalar $(θ)$. This condition leads to $A=B^{n}$, where $A$ and $B$ are metric functions and $n$ is a positive constant giving the proportionality condition between shear and expansion scalar. It has been found that the isotropic distribution of magnetized dark energy leads to the present accelerated expansion of the Universe and the derived model is in good agreement with the recent astrophysical observations. The physical behavior of the Universe has been discussed in details.

physics.gen-ph↗

arXiv2012

The (2+1)-dimensional charged gravastars

This is a continuation and generalization of our earlier work on {\it gravastar} in (2+1) anti-de Sitter space-time to 2+1 dimensional solution of charged gravastar. Morphologically this gravastar contains three regions namely: (i) charged interior, (ii) charged shell and (iii) electrovacuum exterior. We have studied different characteristics in terms of Length and Energy, Entropy, and Junction conditions of the spherical charged distribution. It is shown that the present model of charged gravastar is non-singular and represents itself an alternative of Black Hole.

physics.gen-ph↗

arXiv2012

Galactic rotation curves inspired by a noncommutative-geometry background

This paper discusses the observed at rotation curves of galaxies in the context of noncommutative geometry. The energy density of such a geometry is diffused throughout a region due to the uncertainty encoded in the coordinate commutator. This intrinsic property appears to be sufficient for producing stable circular orbits, as well as attractive gravity, without the need for dark matter.

gr-qc↗