Black star

A black star is a type of star which has a high gravity field.

In 2267, the USS Enterprise encountered two black stars over the course of a number of months. In the first encounter with a black star, the Enterprise was able to escape from the gravitational field, but was backwards in time to the 1960s. (TOS episode: "Tomorrow is Yesterday").

In the second encounter the Enterprise became ensnared in the gravitational field of the star and faced certain destruction. However, Ensign Pavel Chekov was able to plot a course out of the star's gravity field and save the ship. (TOS short story: "Indomitable").