Tides and traversability in gravastars and other related geometries

Tidal effects related to the traversability across thin shells are examined in spherically symmetric geometries. We focus mainly on shells separating inner from outer regions of gravastars (de Sitter — i.e. [Formula: see text] — interior and Schwarzschild exterior of mass parameter M), but we also examine other related geometries by including the possibility of a negative cosmological constant and, besides, nontrivial topologies where the shell separates two outer regions. The analysis is developed for radially traversing objects and for tides in both radial and transverse directions, which present difficulties of somewhat different nature. Transverse tides across shells which satisfy the flare-out condition are the most troublesome, while shells in trivial topologies, i.e. geometries with one asymptotic region, are more indulgent with the issue of large tides. Besides, contradicting other cases analyzed in the previous works, we find that large radial tides cannot be avoided when traveling across the shell in the gravastar solution, but in nontrivial topologies they can. We study with special attention the traversability in practice of the transition layer in the thin-shell gravastar solution. In particular, a finite object which traverses radially the shell in a gravastar with [Formula: see text] undergoes a compression effect in both the transverse and the radial directions due to the tides associated to the thin layer. The results are interpreted in terms of the total momentum transfer obtained by integrating the travel time of the object.