2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/204921Scalar perturbations can grow during a phantomic cosmological phase as the big rip is approached, in spite of the high accelerated expansion regime, if the equation of state is such that $\frac{p}ρ = α< - {5/3}$. It is shown that such result is independent of the spatial curvature. The perturbed equations are exactly solved for any value of the curvature parameter $k$ and of the equation of state parameter $α$. Growing modes are found asymptotically under the condition $α< - {5/3}$. Since the Hubble radius decreases in a phantom universe, such result indicates that a phantom scenario may not survive longtime due to gravitational instability.Latex file, 6 pagesGeneral Relativity and Quantum CosmologyAstrophysicsHigh Energy Physics - Theorytext