Browsing by Author "Katugampala, K. D. W. J."

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Black holes as boson stars.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Katugampala, K. D. W. J.; De Silva, L. N. K.
Kaup (1968) had shown that spin zero bosons could form stable stars. However, there had been no interest in these stars until the Higgs boson was discovered in 2012. Now there is renewed interest in boson stars. Clark (2017) in an article “holy moley” published in the New Scientist (15th July) considers boson stars and black holes as two different types of objects. As far as black holes are considered it can only be said that the matter collapses in to a singularity. Boson stars on the other hand are made of bosons. The above article considers black holes and boson stars to be two different kinds leading to same observations with respect to certain objects. However, they could be the same with black holes constituting bosons of zero mass. In this paper it is suggested that some stars, may be most stars, constitute ordinary matter, some may constitute fermions and bosons, while some others are boson stars. It is not ruled out that some stars could be made of bosons of zero mass such as gluons and/or gravitons. Some stars could be made of bosons including photons, as stars with photons only have been ruled out. de Silva (1970) had considered time like geodesics in the Schwarzschild metric and found that the energy of a particle of rest mass m0 at a coordinate distance r can be written as m0kc2 where and u being the velocity of the particle in the local frame at rest with respect to the frame at infinity. In recent research we have found that the rest mass of a particle in a rest frame, called the local rest frame at coordinate distance r could be considered as m0 (1-2M/r)1/2 in a Schwarzschild metric, where m0 is the rest mass of the particle at infinity and M is the Schwarzschild mass of the central object. The rest mass of the particle in the local rest frame decreases, and ends up as zero as the particle enters the singularity with velocity. It implies that black holes in a Schwarzschild metric could be considered as objects made of bosons with zero mass and observed at large distances with non zero Schwarzschild mass .
A new cosmological model including inflation, deceleration, acceleration and deceleration again.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Perera, P. V. N. M. C.; Katugampala, K. D. W. J.
Since Perlmutter and Riess (1997; 1998) observed that the Universe expands with an acceleration, many models involving dark energy have been proposed to explain this phenomenon. A family of cosmological models with both acceleration and deceleration are presented in this research. Einstein’s Field Equations in General Relativity is written in the form, Here Λ is cosmological constant. The Einstein’s Field Equations are modified. Λ is considered as a variable of cosmic time. The assumptions of a homogeneous and isotropic universe based on the Mach’s principal are made. The Robertson-Walker metric in spherical polar coordinates are started. The Christoffel symbols were found to define the Ricci tensor, the curvature scalar and the energy-momentum tensor using the Robertson-Walker metric. Using the Robertson-Walker metric and Energy momentum tensor are solved modified Einstein’s Field Equations for scalar factor which is called “radius of the universe’’. The solution is introduced in the following form, so that it shows the inflation at the beginning. ......√(1−cos3ωt) A solution is assumed for the universe which results in inflation, deceleration, acceleration and deceleration again. The age of the universe is estimated to be 13.7 billion years. Taking the present value of the cosmic time ....as 13.7 billion years the density of the inflationary Universe is found as 2.0211×10−31.......−3 and deceleration of the Universe as 9.1822×105 ......−2 which are in agreement with the observations. The redshift of light from extragalactic sources, which arise from the Robertson-Walker metric was discussed. This redshift is a measure of the expansion of the universe in a given period of time. The redshift is the ratio of the value of the scalar factor of the universe at present epoch to that at the epoch of emission of light from the extragalactic sources which is observed at present. The scalar factor is increasing with time ... at present. However there could be epochs where the scalar factor is decreasing.
Some properties of expanding universe with variable lambda ()
(Faculty of Science, University of Kelaniya, Sri Lanka, 2021) Karunathilaka, E. L. N. L.; Katugampala, K. D. W. J.
When the Universe is expanding, some of its properties radius, density, volume and total mass would be changed with cosmic time. Those changes can be obtained by using experimental data or solving suitable mathematical models related to the expansion of the Universe. The main purpose of this study is to obtain numerical values of significant properties of expanding Universe by using an appropriate model solution of R (radius of the Universe). Robertson Walker metric and Einstein’s field equations were used as major equations to obtain expressions. This research has been initiated with the Robertson Walker metric in spherical polar coordinates, and it was mainly used to obtain the non-vanishing Christoffel symbols and Ricci tensor components to obtain expressions related to the calculations. Furthermore, all the calculations were depended on four-dimensional space-time coordinates. The pressure of the Universe is considered as zero, and the Universe is assumed to be spherical. Three boundary conditions were used to simplify the numerical values and to obtain expressions related to the properties of the Universe. Moreover, the total mass is a combination of dark matter and ordinary matter. Therefore, boundary conditions were used to separate that two matter masses. Then the values for radius, density, volume and total mass of the Universe were calculated as 1.138527×1028cm, 1.458810-31gcm-3, 6.17871084cm3 and 9.0135×1053g, respectively. Furthermore, ordinary matter mass was obtained as 2.70411053g. These numerical values were similar to the available observed data of the Universe, and they can be used to explain the expansion evidence of the Universe. Hence, the used model solution and the selected redshift value can be used to explain these significant properties of the Universe. The redshift value 1.17 was satisfied the accelerating expansion of the Universe in the present epoch. However, the redshift value can be increased by modifying the solution model of R and then, can be obtained more accurate values. Moreover, this used model can explain not only the present epoch but also the past image and the future image of the Universe.