In Star Trek (2009), red matter is used to create an artificial black hole.
The substance is a powerful fictional material carried by Spock in the film’s alternate-timeline story. When a small quantity is introduced into a planetary or stellar core, it creates a black hole. Spock uses red matter in an attempt to prevent a supernova from destroying Romulus, but the plan comes too late to save the planet and instead helps trigger the film’s changed timeline.
Later in the film, Nero uses red matter to create an artificial black hole near a world. The resulting gravitational phenomenon threatens the surrounding area and becomes central to the conflict between Nero’s mining vessel and the USS Enterprise.
Red matter is sometimes confused with ordinary black holes or with the film’s separate use of exotic mining technology. It is not a real astronomical substance; it is a fictional plot device that gives the 2009 film a mechanism for time travel and alternate-history divergence.