2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/213430The equation of circular loops of cosmic string with time-dependent tension is studied in the Minkowski spacetime and Robertson-Walker universe. We find that, in the case where the tension depends on some power of the cosmic time, cosmic string loops with time-varying tension should not collapse to form a black hole if the power is lower than a critical value.8 pages, 3 figures. accepted by Modern Physics Letters AHigh Energy Physics - Theorytext