Black holes are dangerous space bodies that are invisible, because anything crossing their event horizon simply disappeared. Just short of the horizon there was a shimmering band of a fiery, incandescent brilliance as stray particles accelerating up to light speed glowed.
The gravitational fields near a black hole, or in a black hole system, were highly unpredictable. It was dangerous orbiting a black hole, even 5 billion clicks away from the its event horizon. Confed Fleet regulations allowed their craft to jump into a black hole system only during hot pursuit of an enemy.
The exits of the jump points had the characteristic of shifting randomly, making the safety of arrival a gamble: supposedly on occasion if a ship would come through the jump when it shifted over the event horizon line, immediately it would be sucked in and disappeared.