• Ranjan Sharma

      Articles written in Pramana – Journal of Physics

    • Non-adiabatic radiative collapse of a relativistic star under different initial conditions

      Ranjan Sharma Ramesh Tikekar

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      We examine the role of space-time geometry in the non-adiabatic collapse of a star dissipating energy in the form of radial heat flow, studying its evolution under different initial conditions. The collapse of a star filled with a homogeneous perfect fluid is compared with that of a star filled with inhomogeneous imperfect fluid under anisotropic pressure. Both the configurations are spherically symmetric. However, in the latter case, the physical space 𝑡 = constant of the configurations endowed with spheroidal or pseudospheroidal geometry is assumed to be inhomogeneous. It is observed that as long as the collapse is shear-free, its evolution depends only on the mass and size of the star at the onset of collapse.

    • A family of solutions to the Einstein–Maxwell system of equations describing relativistic charged fluid spheres


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      In this paper, we present a formalism to generate a family of interior solutions to the Einstein–Maxwell system of equations for a spherically symmetric relativistic charged fluid sphere matched to the exterior Reissner–Nordström space–time. By reducing the Einstein–Maxwell system to a recurrence relation with variable rational coefficients, we show that it is possible to obtain closed-form solutions for a specific range of model parameters. A large class of solutions obtained previously are shown to be contained in our general class of solutions. We also analyse the physical viability of our new class of solutions.

    • Models for charged relativistic spheres via hyper-geometric equations


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      Exact solutions to Einstein–Maxwell systems play an important role in relativistic astrophysics. In this paper, a new technique to generate exact solutions to the Einstein–Maxwell system is proposed. Corresponding to a spherically symmetric charged fluid sphere, by specifying the electric field and for a particular form of the metric potential grr , a new solution is obtained in terms of hypergeometric functions. Subsequently, for specific choice of model parameters, many closed-form solutions are developed. In the process, it is possible to regain a number of well-known stellar models which had been developed earlier with or without the presence of charge following the Vaidya and Tikekar ansatz for compact stars (J. Astrophys. Astron. 3:325 (1982); J. Math. Phys. 31:2454 (1990)).It is shown that the new class of solutions can be used as viable models for compact stars for a wide range of values of the model parameters. Physical behaviour of the resultant stellar configurations are studied.

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