Graphic of an energy vortex
An energy vortex is a spinning, turbulent local temporal continuum anomaly comprised of pure energy that occurs in space. Some energy vortexes have enough gravitational force to pull in a Galaxy class starship traveling at maximum warp. Although an energy vortex can destroy a Class-1 probe, shuttlecraft have been known to enter the vortex and travel backwards in time relatively unscathed.
In 2365, the USS Enterprise-D encountered an energy vortex in the Endicor system. This vortex seemed to be sentient, and caused a duplicate version of Captain Picard to appear from six hours in the future. (TNG: "Time Squared")