Browsing by Author "Ibohal, Ng."

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Charged black holes in vaidya backgrounds: Hawkings's radiation
(2010-12-25) Ibohal, Ng.; Kapil, L.
In this paper we propose a class of embedded solutions of Einstein's field equations describing non-rotating Reissner-Nordstrom-Vaidya and rotating Kerr-Newman-Vaidya black holes. The Reissner-Nordstrom-Vaidya is obtained by embedding Reissner-Nordstrom solution into non-rotating Vaidya. Similarly, we also find the Kerr-Newman-Vaidya black hole, when Kerr-Newman embeds into the rotating Vaidya solution. The Reissner-Nordstrom-Vaidya solution is type D whereas Kerr-Newman-Vaidya metric is algebraically special type II of Petrov classification of space-time. These embedded solutions can be expressed in Kerr-Schild ansatze on different backgrounds. The energy momentum tensors for both non-rotating as well as rotating embedded solutions satisfy the energy conservation equations which show that they are solutions of Einstein's field equations. The surface gravity, area, temperature and entropy are also presented for each embedded black hole. It is observed that the area of the embedded black holes is greater than the sum of the areas of the individual ones. By considering the charge to be a function of radial coordinate it is shown that there is a change in the masses of the variable charged black holes. If such radiation continues, the mass of the black hole will evaporate completely thereby forming `instantaneous' charged black holes and creating embedded `negative mass naked singularities' describing the possible life style of radiating embedded black holes during their continuous radiation processes.
Newman-Janis algorithm revisited I: Want-Wu functions and rotating solutions in General Relativity
(2011-07-06) Ibohal, Ng.
In this paper an application of newman-Janis algorithm in spherical symmetric metric with the mass function M (u, r) and the charge e (u, r) has been discussed. after the transformation of the metric via this algorithm, these two functions M(u, r)...............
Newman-Janis algorithm revisited II: Hawking radiation of the variable-charged black holes embedded in de sitter spaces
(2011-07-06) Ibohal, Ng.
Non-stationary de Sitter cosmological models
(2009-01-01) Ibohal, Ng.
In this note it is proposed a class of non-stationary de Sitter, rotating and non- rotating, solutions of Einstein’s ﬁeld equations with a cosmological term of variable function Λ∗(u). It is found that the space-time of the rotating non-stationary de Sitter model is an algebraically special in the Petrov classiﬁcation of gravitational ﬁeld with a null vector, which is geodesic, shear free, expanding as well as non-zero twist. However, that of the non-rotating non-stationary model is conformally ﬂat with non-empty space.
On the Variable-charged Black Holes Embedded into de Sitter Space: Hawking's Radiation
(2011-07-06) Ibohal, Ng.
In this paper we discuss the Hawking’s evaporation of the masses of variable-charged Reissner-Nordstromand Kerr-Newman, black holes embedded into the de Sitter cosmological universe by considering the charge to be function of radial coordinate. It has been shown that every electrical radiation of variable-charged rotating or non-rotating cosmological black holes will produce a change in the mass of the body without eﬀecting the Maxwell scalar and the cosmological constant. It is also shown that during the Hawking’s radiation process, after the complete evaporation of masses of both variable-charged Reissner- Nordstrom-de Sitter and Kerr-Newman-de Sitter black holes, the elec- trical radiation will continue creating negative mass naked singularities embedded into de Sitter cosmological spaces de Sitter black holes
Rotating embedded black holes: Entropy and Hawking's radiation
(2011-07-06) Ibohal, Ng.
In this paper, by applying Newman-Janis algorithm to a spherically symmetric ‘seed’ metric, we present general rotating metrics in terms of Newman-Penrose (NP) quantities involving Wang-Wu func- tions. From these NP quantities we present a class of rotating solutions including (i) Vaidya-Bonnor, (ii) Kerr-Newman-Vaidya, (iii) de Sitter, (iv) Kerr-Newman-Vaidya-de Sitter and (v) Kerr-Newman- monopole. The rotating Kerr-Newman-Vaidya solution represents a black hole that the Kerr-Newman black hole is embedded into the rotating Vaidya radiating universe. In the case of Kerr-Newman-Vaidya- de Sitter solution, one can describe it as the Kerr-Newman black hole is embedded into the rotating Vaidya-de Sitter universe, and similarly, Kerr-Newman-monopole. We have also discussed the physical properties by observing the energy momentum tensors of these solutions. These embedded solutions can be expressed in Kerr-Schild forms describing the extensions of Glass and Krisch superposition, which is further the extension of Xanthopoulos superposition. It is shown that, by considering the charge to be a function of radial coordinate, the Hawking’s continuous radiation of black holes can be expressed in classical spacetime metrics for these embedded black holes. It is also found that the electrical radiation will continue to form ‘instantaneous’ charged black holes and creating embedded negative mass naked singularities describing the possible life style of radiating embedded black holes during their contineous radiation processes. The surface gravity, entropy and angular velocity, which are important parameters of a horizon, are also presented for each of the embedded black holes.
Rotating metrics admitting non-perfect fluids in General Relativity
(2011-07-06) Ibohal, Ng.
In this paper an application of Newman-Janis algorithm in spherical sym- metric metrics with the functions M(u, r) and e(u, r) has been discussed. After the transformation of the metric via this algorithm, these two functions M(u, r) and e(u, r) will be of the three variables u, r, θ. With these functions of three variables, all the Newman-Penrose (NP) spin coeﬃcients, the Ricci as well as the Weyl scalars have been calculated from the Cartan’s structure equations. From these NP quantities, a class of rotating solutions of Einstein’s ﬁeld equa- tions can be obtained. These solutions include (a) Kerr-Newman, (b) rotating Vaidya solution, (c) rotating Vaidya-Bonnor solution, (d) rotating Husain’s solution, (e) rotating Wang-Wu solutions. It is found that the technique de- veloped by Wang and Wu can be used to generate new embedded solutions, that the Kerr-Newman solution can be combined smoothly with the rotating Vaidya solution to generate Kerr-Newman-Vaidya solution, and similarly, Kerr- Newman-Vaidya-Bonnor solution of the ﬁeld equations. It has also shown that the embedded universes like Kerr-Newman de Sitter, rotating Vaidya-Bonnor- de Sitter, Kerr-Newman-Vaidya-de Sitter can be derived from the general so- lutions with Wang-Wu function. All rotating embedded solutions derived here can be written in Kerr-Schild forms, showing the extension of Xanthopoulos’s theorem. It is also found that all the rotating solutions admit non-perfect ﬂuids.