A wrap star.
A warp star was a small diamond-shaped device attached to a pendant which contained enough energies within its small form to create a powerful explosion. According to Jack Harkness, it was a warp fold conjugation trapped in a carbonised shell, or an "explosion waiting to happen".
Sarah Jane Smith was given a warp star by a Verron soothsayer. After she escaped the Daleks on the Crucible, she informed Jack that she possessed it. They planned on detonating the device within the New Dalek Empire's Crucible, thus crippling it. However, the Daleks used a transmat beam to quickly remove the threat by capturing Sarah Jane and Jack, as well as Jackie Tyler and Mickey Smith. (TV: Journey's End)
Behind the scenes
- Five different warp star designs were originally presented. This design used was chosen with Sarah Jane's character in mind.