Black star

From Memory Alpha, the free Star Trek reference

Black star was a type of star that had high gravitational attraction. They could remain undetected until encountered by entering their gravity field.

In 2267, the USS Enterprise, en route to Starbase 9 for resupply, was dragged towards the gravity of a previously unknown black star in the area of the base. While using all available warp power in reverse to escape the star, the breakaway sent the Enterprise into a time warp due to the slingshot effect. The whiplash threw the starship almost three centuries backward through time and to a low atmospheric orbit around Earth, as the Sol system was located in the heading they were pulling away to. (TOS: "Tomorrow is Yesterday")