Phantom stars and topology change

In this work, we consider time-dependent dark-energy star models, with an evolving parameter !
crossing the phantom divide ! ¼ 1. Once in the phantom regime, the null energy condition is violated,
which physically implies that the negative radial pressure exceeds the energy density. Therefore, an
enormous negative pressure in the center may, in principle, imply a topology change, consequently
opening up a tunnel and converting the dark-energy star into a wormhole. The criteria for this topology
change are discussed and, in particular, we consider a Casimir energy approach involving quasilocal
energy difference calculations that may reflect or measure the occurrence of a topology change.We denote
these exotic geometries consisting of dark-energy stars (in the phantom regime) and phantom wormholes
as phantom stars. The final product of this topological change, namely, phantom wormholes, have farreaching
physical and cosmological implications, as in addition to being used for interstellar shortcuts, an
absurdly advanced civilization may manipulate these geometries to induce closed timelike curves,
consequently violating causality.