Debadri Bhattacharjee, Pradip Kumar Chattopadhyay

This study investigates the gravastars in the framemwork of Rastall theory of gravity in generalised cylindrically symmetric space-time. Following the Mazur-Mottola hypothesis (P. O. Mazur and E. Mottola, Universe {\bf 9}, 88 (2023)), gravastars are classified as one of the most unique and exotic kind of compact objects, presenting themselves as a plausible alternative to black holes. In this study, we build upon the Mazur-Mottola framework of Gravitational Bose-Einstein Condensate (GBEC) stars by generalising it to a cylindrically symmetric spacetime within the framework of Rastall gravity to present a novel approach for estimating the mass limit of the thin shell of isotropic gravastars. We have ensured singularity-free solutions for the interior de-Sitter core, non-vanishing solutions for the thin shell and flat vacuum solution of the exterior region, within this parameter space. Under the framework of Rastall gravity and cylindrically symmetric spacetime, the Lanczos equations at the hypersurface junction $(r=R)$ undergo significant modifications, leading to a revised form of the Darmois-Israel junction conditions. These modified junction conditions are utilised to investigate the influence of the Rastall parameter $(\xi)$ on the mass of the thin shell and key characteristics of gravastars, including the shell's proper length, energy, and entropy. Additionally, we propose a novel method for estimating the mass of the thin shell using the concept of surface redshift $(Z_{s})$. By adhering to the Buchdahl upper limit, $Z_{s}<2$ for isotropic configuration, we have determined the mass bounds of the thin shell for various characteristic radii and values of the Rastall parameter $(\xi)$.