If you can create a space warp, you can create much, much more gravity than a star. Of course, we are talking apples and oranges, because the question isn't really about how much, as about how much in what amount of space. In any event, I'm not saying a gravity field would be used -- that would be attractive
. I'm saying a negative energy and/or exotic matter-generated antigravity
field. A repulsive
field. Remember, the purpose of such a field is to keep open the fabric of space that has been warped by intense gravity -- a microsingularity or some other source -- at the ship's bow. Absent an antigravity field amidships, the fabric of space would collapse and create (I think) a black hole. The ship would be destroyed. The antigravity keeps the "throat" open, and creates something akin to (again, I think) a wormhole. The ship then has another hypergravity source at the stern to close the breach and restore the fabric of space to its natural geometry.