A warp star was a small diamond-like device that could create a powerful explosion. Jack Harkness described it as a warp fold conjugation trapped in a carbonised shell, or an “explosion waiting to happen”.
Sarah Jane Smith was given a warp star on a pendant by a Verron soothsayer. After escaping Dalek captivity on the Crucible, she and Jack planned to detonate it to destroy the space station. However, the Daleks used a transmat beam to quickly remove Sarah Jane and Jack from the warp star, neutralising the threat. (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.