Cauchy horizons in Gowdy space times

We analyse exhaustively the structure of \emph{non-degenerate} Cauchy horizons in Gowdy space-times, and we establish existence of a large class of non-polarized Gowdy space-times with such horizons. Added in proof: Our results here, together with deep new results of H. Ringstr\"om (talk at the Miami Waves conference, January 2004), establish strong cosmic censorship in (toroidal) Gowdy space-times.Comment: 25 pages Latex. Further information at http://grtensor.org/gowdy