[Actually, I thought of a way to hide a ship in open space some time ago, but only for a relatively brief interval and only if you don't accelerate. Basically, you deploy a giant umbrella perpendicular to the most likely axis of detection, one that has a heat-reflecting inner surface and an absorptive outer surface. You focus the cone back past your ship, slightly off-center (so that you aren't refocusing the reflected heat back on your ship). But this will only work until the umbrella itself heats up and won't help you at all against detection via visual occlusion (the fact that your ship+umbrella will be blacking out a section of the starfield from the opponent's POV).]

 

Basically, in space if you can see it, you can shoot it. And you can almost always see it.