Micro-wormhole

A micro-wormhole was a wormhole of much smaller size than their counterparts. A micro-wormhole could have originally been of a much greater size, but was in an advanced state of collapse, and over time had degraded and shrunk to a smaller size.

In 2371, the USS Voyager discovered a naturally-occurring micro-wormhole thirty centimeters in diameter. The wormhole led from the Delta Quadrant to Romulan space (in the past). The crew gave the wormhole the name Harry Kim wormhole. 

In 2376, the Pathfinder Project at Starfleet Communications was able to create a temporary, artificial micro-wormhole using the MIDAS array, to briefly communicate with Voyager over 30,000 light years away in the Delta Quadrant. 

Microwormgat