Dark zone
The dark zone was a negative energy field which emanated from the space amoeba.

In 2268, the  encountered this zone which was described by Captain James T. Kirk as a hole in space. It laid directly in line with the course that Lieutenant Commander Spock had calculated for the  and the Gamma 7A solar system, both of which contact had been lost with. A telemetry probe was launched into the zone but was destroyed shortly after.

Spock had insufficient information for an analysis of the dark area. The computers contained nothing on this phenomenon as it was beyond their experience. Unable to determine what it was, Spock determined that it was not liquid, gaseous, or solid despite the fact they could not see through it, and it was also not a galactic nebula such as the Coalsack.

However, since their deflector shields were activated by it, the area seemed to be some form of energy but nothing that could be identified by sensors. Kirk questioned if it was possible that it killed the Gamma 7A system and the Intrepid, which Spock concluded was very possible.

The area of darkness was probed again for further information which resulted in penetrating an unknown boundary layer and entering a zone of energy which was incompatible with their living and mechanical processes. As they drew closer to the source, it grew stronger and they grew weaker. Engines were stopped as they sought a defense against an energy drain which seemed to pervade the zone and absorbed all forms of energy whether mechanically or biologically produced. It was determined that the zone was not the source of the power drain, but rather the space amoeba was. ()

See also
Hole in space
Regions
Energy fields