When ships use their Jump Drives to travel from star to star, they always pass through a mysterious, strange void known as jump space. The amount of time spent in jump space is proportional to the distance between the stars.
System jump technology was humanity's first means of interstellar travel. The Alliance possesses means of communication between ships in jump space, but only some information can be sent. The Syndicate Worlds do not possess this ability. Since the discovery of the Hypernet, there has been little research into jump space, so little is known about it. Random flashes of light can be seen in jump space, but its cause is unknown. It is generally believed that these lights are ancestors of the crew or "the living stars", and some believe that Geary was among them until he took command of the fleet.
Alliance regulations state the remains of traitors may only be disposed of in jump space. This comes from an episode fifty years back, and Captain Kila's remains were disposed the same way when she was discovered to be the main figure of the Anti-Geary Conspiracy.