IIRC they use "collapsars", which are wormhole-like things that are discovered, not made (or maybe left there by a previous civilization?). They spend weeks and

IIRC they use "collapsars", which are wormhole-like things that are discovered, not made (or maybe left there by a previous civilization?). They spend weeks and months accelerating to and decelerating from collapsars, but I don't think they mention ramjets as a means to accelerate and decelerate in "normal space".