Planar black holes and wormholes with a flat exterior

We present $n(\ge 4)$-dimensional planar black holes and wormholes with a flat exterior, which are originated by an exact solution in general relativity. The nonvacuum regions of these objects are described by the extended dynamical region inside a nondegenerate Killing horizon of Gamboa's static plane symmetric solution with a perfect fluid obeying a linear equation of state $p=\chi\rho$ for $\chi\in[-1/3,0)$. The matter field inside the horizon is not a perfect fluid but an anisotropic fluid that may be interpreted as a {\it spacelike} (tachyonic) perfect fluid. While it satisfies the null and strong energy conditions in the black hole case, it violates all the standard energy conditions in the wormhole case. The metric on the horizon is not analytic but at least $C^{1,1}$ in the single-null coordinates in both cases, so it is regular and there is no lightlike massive thin shell on the horizon.