Solutions of the Einstein–Maxwell equations with energy–momentum tensor for polytropic core and linear envelope

S. A. Mardan; A. Khalid; Sana Saleem; Muhammad Bilal Riaz

doi:10.1140/epjc/s10052-025-13890-y

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2023 Impact factor 4.2

Particles and Fields

Open Access

Eur. Phys. J. C (2025) 85: 177
https://doi.org/10.1140/epjc/s10052-025-13890-y

Regular Article - Theoretical Physics

Solutions of the Einstein–Maxwell equations with energy–momentum tensor for polytropic core and linear envelope

S. A. Mardan¹, A. Khalid¹^,3^a, Sana Saleem¹ and Muhammad Bilal Riaz²^,3

¹ University of Management and Technology, C-II Johar Town, Lahore, Pakistan
² VSB-Technical University of Ostrava, IT4Innovations, Ostrava, Czech Republic
³ Jadara University Research Center, Jadara University, Jordan

^a ayeshakhalid4238@gmail.com, S2019109012@umt.edu.pk

Received: 16 October 2024
Accepted: 2 February 2025
Published online: 12 February 2025

Abstract

Investigating an anisotropic charged spherically symmetric core-envelope model for dense star objects is the aim of this paper. The polytropic equation of state (EoS) defines the core of this model, while the linear EoS represents the envelope. The radiation density-containing energy–momentum tensor is used to determine the solution of the Einstein–Maxwell field equations. All three regions-core, envelope, and Reissner Nordström external metric-have perfect matching. For the intrinsic structure of the stars $S A X J 1808.4 - 3658$ $$SAX~J1808.4-3658$$ and $4 U 1608 - 52$ $$4U1608-52$$ , the model is physically feasible. Additionally, the Tolman–Oppenheimer–Volkoff (TOV) equation is used to verify the equilibrium state, and the adiabatic index is used to verify stability.

© The Author(s) 2025

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