The anomaly known as "the Void" was a closed structure in the Delta Quadrant, encased in an inert layer of subspace. Approximately nine light years in circumference, it was impenetrable to matter or energy, resulting in a region wherein no gases, stellar bodies, or matter of any kind existed. Within the Void, funnels periodically erupted into normal space, creating massive graviton forces which would pull in any ship unfortunate enough to be in the vicinity. Inside, the same graviton forces acted to drain a vessel's power supply, making energy a highly-limited commodity. This resulted in a number of crews trapped within the Void turning to piracy and murder.
In 2377, the USS Voyager was pulled into the Void and immediately came under attack by vessels who preyed on new arrivals for food and supplies. The Voyager crew was able to fend off the attacks and made contact with a species that was apparently native to the Void. Utilizing Borg sensors, the crew discovered that, when the graviton forces reached critical levels, the polarity suddenly reversed, pulling anything near the funnel inside. The crew developed a plan whereby they would enter a funnel just as it was forming, and jump to high warp immediately before the polarity reversed. However, as they had no way of compensating for the graviton stress, they were forced to construct a polaron modulator with the help of other crews who had agreed to cooperate in planning an escape. Eventually, their plan was successful, and Voyager and the other vessels were able to return to normal space. (VOY: "The Void")