Nexus



The Nexus is a nonlinear temporal phenomenon which can be entered via a temporal flux energy ribbon which crosses the Galaxy every 39 years. It is possible that the ribbon was created by a young Q billions of years ago. (TNG novel: Q-Space)

First known contact with the Nexus was made in 2293 by a group of El-Aurian refugees, including Guinan and Tolian Soran. The refugees were rescued by the USS Enterprise-B, but at the apparent cost of the life of James T. Kirk. (movie: Star Trek Generations)

In 2332, Guinan was visiting Oblivion when the Nexus energy ribbon again crossed through the Galaxy. She felt it even 3,000 kilometers from the orbital city, reopening old wounds for her. (Stargazer novel: Oblivion)

In 2371, Soran, having become obsessed with returning to the Nexus, committed several criminal acts in an attempt to bring the Nexus to Veridian III, having determined there was no guaranteed safe way to approach it by ship. Soran was defeated by Captain Jean-Luc Picard and Kirk, though at the cost of the latter's death and the destruction of the USS Enterprise-D. (movie: Star Trek Generations)

The Nexus in Alternate Timelines
In one alternate timeline, Montgomery Scott traveled from 2370 to 2293 to beam Kirk from the Enterprise-B just before he was pulled into the Nexus. This altered history so that the Borg invasion of 2063 Earth was successful. (TNG novel: Engines of Destiny)