Wormholes: Controlling exotic matter with a magnetic field

In this work the junction condition formalism is used to build up wormholes from two identical spacetimes, which are exact solutions of the Einstein-Maxwell equations. The surgery produces a class of wormholes in which the amount of exotic matter is controlled by an external magnetic field. It is demonstrated that the total amount of exotic material is a decreasing function of the magnetic field intensity and that most of the remaining material is concentrated near the poles of the junction. A region in which there is no violation of the null and strong energy conditions is determined. The range of applicability of the model is discussed in some detail.