(Journal of Experimental and Theoretical Physics, Springer Link, 2016) Rubab Manzoor
This paper investigates instability ranges of a cylindrically symmetric collapsing cosmic filamentary structure in Brans-Dicke theory of gravity. For this purpose, we use perturbation approach in the modified field equations as well as dynamical equations and construct a collapse equation. The collapse equation with adiabatic index (Γ) is used to explore the instability ranges of both isotropic as well as anisotropic fluid in Newtonian and post-Newtonian approximations. It turns out that the instability ranges depend on the dynamical variables of collapsing filaments. We conclude that the system always remains unstable for 0 < Γ < 1 while Γ > 1 provides instability only for the special case.