Some extremely old wormholes in an advanced state of decay collapse in on themselves, leaving only a tiny corridor between different parts of the galaxy.
Most wormholes are unstable, and fluctuate wildly between many points in normal space; however, there are some rare examples of stable wormholes.
In 2371, on stardate 48579.4, the crew of the USS Voyager NCC-74656 discovered a stable wormhole. Because Voyager was lost in the Delta Quadrant, the wormhole offered the possibility of a much faster way back to the Alpha Quadrant. But this spatial singularity exhibited some properties not commonly associated with wormholes.
The crew first detected the wormhole when Voyager's sensors registered verteron emanations and tunneling secondary particles on extreme long-range subspace bands. Although it was not clear at first whether these readings indicated the presence of a wormhole, Captain Janeway decided that they were significant enough to warrant further investigation. When Voyager arrived at the anomalous reading's coordinates, the crew discovered that it was indeed a wormhole, but one of a type never before encountered by a Starfleet vessel.
The wormhole appeared to be extremely ancient and in an advanced state of decay; it had most likely been collapsing in on itself for several centuries. It would best be described as a micro-wormhole, since it had mostly dissipated, leaving an extremely narrow passageway through subspace. In fact, the aperture of the wormhole was only about 30 centimeters in diameter, far too small for a vessel to traverse. The micro-wormhole's great age had caused extremely powerful gravitational eddies to develop in its interior.
Because the wormhole's aperture was so small, the crew were not able to determine where it exited, but they could gather data by launching a microprobe, which was only a few centimeters in diameter itself, into the interior of this minute phenomenon. Because of the extremely constricted spatial dimensions of the interior, and the strong gravitational currents, the probes became trapped midway on its journey through the wormhole. Efforts to free it proved futile, but despite being stuck it till functioned for more than 72 hours. The data that it relayed back to Voyager indicated that the far end of the wormhole terminated in the Alpha Quadrant. It also indicated a strange phase variance in the radiation stream that was at first of unknown origin.
Although Voyager was unable to pass through the wormhole, Ensign Harry Kim managed to use the trapped microprobe as an amplifying relay station to send a signal.
The data transfer rate was extremely limited and the phase variance made it difficult to transmit a clean signal, but the crew managed to boost the signal enough to establish communication with a vessel in the Alpha Quadrant. It was received by the Romulan science vessel Talvath, commanded by Telek R'Mor, operating near the Alpha Quadrant terminus of the wormhole in sector 1385.
After communications were established with the Talvath, Voyager's chief engineer, B'Elanna Torres, realized that the phase amplitude of the visual link with the Romulan ship was within a few megahertz of meeting transporter protocols and that it was feasible to piggyback a transporter beam onto it. The transport involved substantially modifying the matter transmission rate, and matching the data transmission to the phase amplitude of the Romulan comm signal.
The first transport involved a test cylinder, which had a varietal molecular matrix that simulated most organic and non-organic compounds. There were some complications, but the transport proved a success. R'Mor was then transported through the wormhole to Voyager, with equally impressive results. This meant that technically the entire crew could be transported via the probe to the Alpha Quadrant using this technique.
Unfortunately for the crew of Voyager, it was discovered that the strange phase variance discovered earlier was a by-product of the fact that this micro-wormhole not only traversed space but time as well. The crew determined that the Alpha Quadrant terminus of the micro-wormhole was located 20 years in the past.
Captain Janeway decided that it would disrupt the timeline if she allowed Voyager's crew to transport themselves back in time, but R'Mor agreed to take message back through the wormhole and deliver them to Starfleet and the families of Voyager's crew when the time was right. Unfortunately, Telek R'Mor died in 2367, four years before he was due to deliver the messages.
In 2376, Starfleet engineer Reginald Barclay, working on the Pathfinder project, managed to create a micro-wormhole by directing a 60-terawatt tachyon beam from the Mutara Inter-dimensional Deep Space Transponder Array (MIDAS) at a Class-B itinerant pulsar. The beam eventually produced a gravimetric surge that was powerful enough to generate a tiny wormhole.
Barclay was able to move the micro-wormhole's exit point to the specific locations by altering the phase alignment of the tachyon beam. He succeeded in sending a message through the micro-wormhole and managed to briefly establish communication with Voyager, thousands of light years away from Earth.This article comes from Star Trek Magazine, v. 1, i. 12.