Redemption Ark (Revelation Space, #2) by Alastair Reynolds

Late in the twenty-sixth century, the human race has advanced enough to accidentally trigger the Inhibitors - alien killing machines designed to detect intelligent life and destroy it. The only hope for humanity lies in the recovery of a secret cache of doomsday weapons -and a renegade named Clavain who is determined to find them. But other factions want the weapons for their own purposes - and the weapons themselves have another agenda altogether…