Browsing by Author "Sunzu, Jefta M."
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Item Charged anisotropic composite stellar object with strange, polytropic and gaseous matter(Elsevier, 2024-08) Olengeile, Lilian; Sunzu, Jefta M.; Mkenyeleye, Jason M.In this study, we build a charged star model with three layers with distinct equations of state. The core, intermediate layer, and envelope layer obey linear, polytropic, and Chaplygin equations of state, respectively. The model satisfies the physical requirements for the matter variables, gravitational potentials, and stability conditions. We have generated within-acceptable range masses and radii for stars. We also recover the masses and radii for the stars PSRJ1903+0327, PSRJ1614-2230, SAXJ1808.4-3658, Vela X-1, and EXO1785-248 from earlier investigations which shows astrophysical significance of our model.Item Charged anisotropic models via embedding(Springer, 2021) Mathias, Alberto K.; Maharaj, Sunil D.; Sunzu, Jefta M.; Mkenyeleye, Jason M.We generate exact solutions to the Einstein–Maxwell field equations by analysing the embedding condition. We obtain a relationship between gravitational potentials that helps to solve the embedding condition and integrate the field equations. Our choice of the measure of anisotropy and electric field are physically realistic. Our model contains several previously known solutions as special cases. These include the investigations of interior Schwarzchild metric, Finch and Skea, Hansraj and Maharaj, Feroze and Siddiqui, and Manjonjo, Maharaj and Moopanar. We also describe the structure and properties of the relativistic star by including graphical representations. Our analysis shows that the body is stable, all energy conditions are satisfied, the regularity condition is not violated, forces under equilibrium condition are balanced, all matter variables are well behaved and the matching conditions are satisfied at the boundary of the relativistic star.Item Core-envelope anisotropic star model admitting Karmarkar condition(Elsevier BV, 2024) Mathias, Amos V.; Sunzu, Jefta M.; Mkenyeleye, Jason M.We generate a neutral core-envelope stellar model with anisotropic fluid distribution which admits Karmarkar condition. The core and envelope layers are assumed to compose quark matter and neutron fluid consistent with linear and quadratic equations of state, respectively. The results obtained indicate that the present model conforms with physical and stability tests. In the present model we have generated radii and masses of astrophysical objects consistent with observations such as HerX-1, 4U 1538-52 and SAX J1808.4-3658. It is interesting to note that the study of multilayered stars in Karmarkar condition is missing in the stellar models generated in the past.Item Detailed characterisation of LINERs and retired galaxies in the local universe(Cambridge University Press, 2021) Mazengo, Daudi T.; Pović, Mirjana; Jiwaji, Noorali T.; Sunzu, Jefta M.We present a detailed characterisation of physical properties of low-ionization nuclear emission-line regions (LINERs) and retired galaxies (RGs) in the local universe for redshift range 0 < z < 0.4 and two subranges z < 0.4 and 0.1 < z < 0.4. Furthermore, we test the effectiveness of WHAN diagnostic diagram in separating the two populations. We used photometric data, public spectroscopic data and morphological classification from SDSS-DR8, MPA-JHU SDSS-DR8 catalogue and Galaxy Zoo survey, respectively. We studied the distribution of LINERs, RGs and AGN-LINERs in relation to luminosity, stellar mass, star formation rate (SFR), colour, and their location on the SFR-stellar mass and colour-stellar mass diagrams. We then studied the morphologies of both populations. Results have shown that for higher redshift range, AGN-LINERs have higher apparent g magnitude, SFRs and dominate on/above the main sequence (MS) of star formation compared to RGs. However, both populations have similar stellar mass and luminosity distributions at all redshift ranges hence suggesting a significant difference in terms of star formation of RGs and AGN-LINERs with redshift. However, larger and more complete samples of LINERs are needed from the future surveys (e.g., LSST) and missions (e.g., JWST) to study in more details the properties of RGs and AGN-LINERs and find alternative methods of separating the two populations, since using simply WHAN diagram from our study we do not find it to be effective for separating the two populations.Item A generalised double layered model with polytropic and quadratic equations of state(Elsevier, 2023) Sunzu, Jefta M.; Lighuda, Avirt S.This study generates a new exact model for a massive stellar spheres by utilising the Einstein–Maxwell field equations. The model has two interior regions with distinct equations of state (EoS): the polytropic EoS at the core region, and quadratic EoS at the envelope region. Variation of the physical features in the interior of star affirms that the matter variables, gravitational potentials and other physical quantities are consistent with massive stellar bodies. Interestingly, our model can regain solutions of the two-layered model generated by Mardan, Noureen and Khalid. Matching of the layers in junctions is done with help of the Reissner–Nordstrom exterior spacetime. Using our model, stellar masses, and radii consistent with observations and well known stars are generated.Item Hall and viscous dissipation effects on mixed convective MHD heat absorbing flow due to an impulsively moving vertical porous plate with ramped surface temperature and concentration(Wiley, 2024) Matao,Paul Majani; Reddy, Bijjula Prabhakar; Sunzu, Jefta M.The current investigation is purported on viscous heating dissipation and Hall consequences on mixed convection magneto‐hydrodynamic heat captivating fluid transmitting from an impulsively starting vertical porous plate with ramp surface temperature and concentration in the existence of chemical reaction and radiation. The dimensional flow dominating partial differential equations is translated into a non‐dimensional partial differential form by adopting appropriate variables and parameters. A finite element approach is driven to simplify the resulting dimensionless nonlinear linked partial differential equations with initial and boundary stipulates. The after‐effects of flow commanding parameters on the velocity components, temperature and concentration are broadly analysed graphically, whereas both primary and secondary shear stresses, heat and mass transferral rates close to the surface area of the plate are discussed in tables. The ultimate results of this research revealed that viscous heating dissipation, Hall current, and thermal and mass buoyancy responses intensify both velocity components, whereas the efficacy of magnetic fields and radiation degrade both velocity components. The temperature distribution devalues with increasing heat absorption and Prandtl number, but a contrary impulse was noted with viscous heating dissipation. Likewise, concentration distribution expands with time progress but decays with chemical reaction parameters. A comparative analysis among the current results and certain research studies in the literature manifests the results’ precision and correctness.Item Hall and viscous dissipation effects on mixed convective MHD heat absorbing flow due to an impulsively moving vertical porous plate with ramped surface temperature and concentration(Wiley, 2024) Matao, Paul Majani; Reddy, Bijjula Prabhakar; Sunzu, Jefta M.The current investigation is purported on viscous heating dissipation and Hall consequences on mixed convection magneto‐hydrodynamic heat captivating fluid transmitting from an impulsively starting vertical porous plate with ramp surface temperature and concentration in the existence of chemical reaction and radiation. The dimensional flow dominating partial differential equations is translated into a non‐dimensional partial differential form by adopting appropriate variables and parameters. A finite element approach is driven to simplify the resulting dimensionless nonlinear linked partial differential equations with initial and boundary stipulates. The after‐effects of flow commanding parameters on the velocity components, temperature and concentration are broadly analysed graphically, whereas both primary and secondary shear stresses, heat and mass transferral rates close to the surface area of the plate are discussed in tables. The ultimate results of this research revealed that viscous heating dissipation, Hall current, and thermal and mass buoyancy responses intensify both velocity components, whereas the efficacy of magnetic fields and radiation degrade both velocity components. The temperature distribution devalues with increasing heat absorption and Prandtl number, but a contrary impulse was noted with viscous heating dissipation. Likewise, concentration distribution expands with time progress but decays with chemical reaction parameters. A comparative analysis among the current results and certain research studies in the literature manifests the results’ precision and correctness.Item A neutral stellar model with quadratic equation of state(Springer, 2022) Sunzu, Jefta M.; Mathias, Amos VWe generate a new exact model for neutral anisotropic star using Einstein field equations. In this model, we consider a quadratic equation of state (QEoS) and a choice of gravitational potential which generalizes the choice formulated by Pant and Fuloria. We generate stellar masses consistent with previous findings which describe the astrophysical objects like PSR J1614-2230, Cen X-3, Vela X-1 and Exo 1785-248. New relativistic stellar masses and surface gravitational redshifts in acceptable ranges are also generated using our model. It is observed that the matter variables and gravitational potentials are well behaved. The model satisfies energy and stability conditions and all forces within the stellar object sum to zero.Item Physical quark star model with generalized logarithmic anisotropy(World Scientific Pub Co Pte Ltd, 2023) Mkenyeleye, Jason M.; Juma, Mahamudu; Sunzu, Jefta M.A new quark star model for a charged anisotropic stellar object is generated using the Einstein–Maxwell field equations. We use a metric function, linear equation of state, and a new measure of anisotropy in form of logarithmic function to formulate the model. For particular choices of parameters in the anisotropic measure, some anisotropic and isotropic models are regained as a special case. Physical analysis indicates that matter variables and gravitational potentials in the model are well behaved. The generated model satisfies the energy, regularity, causality, and stability conditions. The speed of sound is consistent with quark stars.Item Quark star models with logarithmic anisotropy(Springer, 2022) Juma, Mahamudu; Mkenyeleye, Jason M.; Sunzu, Jefta M.New models for the charged anisotropic stellar object were generated using the Einstein–Maxwell field equations. A new choice of pressure anisotropy in logarithmic form was used to generate a quark star model. Anisotropic and isotropic models were regained as a special case. We regained anisotropic models found by Maharaj, Sunzu and Ray; Abdalla, Sunzu and Mkenyeleye; and Sunzu and Danford. The isotropic models regained include the performance by Mak and Harko, and Maharaj and Komathiraj. Physical analysis showed that matter variables and the gravitational potentials are well behaved. Our model does satisfy the energy conditions and stability condition.Item Regular quark star model with pressure anisotropy(Springer, 2022) Mathias, Amos V.; Sunzu, Jefta M.A new regular model for a stellar sphere with quark matter is found. The model satisfies a neutral quark star with pressure anisotropy. In this model, we consider an ansatz of a new form of one of the gravitational potentials, and stellar masses consistent with other findings which describe the generation of astrophysical objects. New masses, radii and surface gravitational red-shifts in acceptable ranges are also obtained using our model. The model satisfies stability and energy conditions. The state of hydrostatic equilibrium for stability is obtained by analysing the Tolman–Oppenheimer–Volkoff (TOV) equation. All other matter variables and gravitational potentials are well behaved.Item A well-behaved anisotropic strange star model(Hindawi, 2022) Mathias, Amos V.; Sunzu, Jefta M.We obtain a new nonsingular exact model for compact stellar objects by using the Einstein field equations. The model is consistent with stellar star with anisotropic quark matter in the absence of electric field. Our treatment considers spacetime geometry which is static and spherically symmetric. Ansatz of a rational form of one of the gravitational potentials is made to generate physically admissible results. The balance of gravitational, hydrostatic, and anisotropic forces within the stellar star is tested by analysing the Tolman-Oppenheimer-Volkoff (TOV) equation. Several stellar objects with masses and radii comparable with observations found in the past are generated. Our model obeys different stability tests and energy conditions. The profiles for the potentials, matter variables, stability, and energy conditions are well behaved